diff --git a/Migrations/0001_01_01_000007_add_template_versions.php b/Migrations/0001_01_01_000007_add_template_versions.php
new file mode 100644
index 0000000..418da01
--- /dev/null
+++ b/Migrations/0001_01_01_000007_add_template_versions.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Create plan_template_versions table and add template_version_id to agent_plans.
+     *
+     * Template versions snapshot YAML template content at plan-creation time so
+     * existing plans are never affected when a template file is updated.
+     *
+     * Deduplication: identical content reuses the same version row (same content_hash).
+     *
+     * Guarded with hasTable()/hasColumn() so this migration is idempotent and
+     * can coexist with a consolidated app-level migration.
+     */
+    public function up(): void
+    {
+        Schema::disableForeignKeyConstraints();
+
+        if (! Schema::hasTable('plan_template_versions')) {
+            Schema::create('plan_template_versions', function (Blueprint $table) {
+                $table->id();
+                $table->string('slug');
+                $table->unsignedInteger('version');
+                $table->string('name');
+                $table->json('content');
+                $table->char('content_hash', 64);
+                $table->timestamps();
+
+                $table->unique(['slug', 'version']);
+                $table->index(['slug', 'content_hash']);
+            });
+        }
+
+        if (Schema::hasTable('agent_plans') && ! Schema::hasColumn('agent_plans', 'template_version_id')) {
+            Schema::table('agent_plans', function (Blueprint $table) {
+                $table->foreignId('template_version_id')
+                    ->nullable()
+                    ->constrained('plan_template_versions')
+                    ->nullOnDelete()
+                    ->after('source_file');
+            });
+        }
+
+        Schema::enableForeignKeyConstraints();
+    }
+
+    public function down(): void
+    {
+        Schema::disableForeignKeyConstraints();
+
+        if (Schema::hasTable('agent_plans') && Schema::hasColumn('agent_plans', 'template_version_id')) {
+            Schema::table('agent_plans', function (Blueprint $table) {
+                $table->dropForeign(['template_version_id']);
+                $table->dropColumn('template_version_id');
+            });
+        }
+
+        Schema::dropIfExists('plan_template_versions');
+
+        Schema::enableForeignKeyConstraints();
+    }
+};
diff --git a/Models/AgentPlan.php b/Models/AgentPlan.php
index 5bb118a..8605b41 100644
--- a/Models/AgentPlan.php
+++ b/Models/AgentPlan.php
@@ -66,6 +66,7 @@ class AgentPlan extends Model
         'metadata',
         'source_file',
         'archived_at',
+        'template_version_id',
     ];
 
     protected $casts = [
@@ -105,6 +106,11 @@ class AgentPlan extends Model
         return $this->hasMany(AgentWorkspaceState::class);
     }
 
+    public function templateVersion(): BelongsTo
+    {
+        return $this->belongsTo(PlanTemplateVersion::class, 'template_version_id');
+    }
+
     // Scopes
     public function scopeActive(Builder $query): Builder
     {
diff --git a/Models/PlanTemplateVersion.php b/Models/PlanTemplateVersion.php
new file mode 100644
index 0000000..a8e5d8c
--- /dev/null
+++ b/Models/PlanTemplateVersion.php
@@ -0,0 +1,92 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Core\Mod\Agentic\Models;
+
+use Illuminate\Database\Eloquent\Collection;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+/**
+ * Plan Template Version - immutable snapshot of a YAML template's content.
+ *
+ * When a plan is created from a template, the template content is snapshotted
+ * here so future edits to the YAML file do not affect existing plans.
+ *
+ * Identical content is deduplicated via content_hash so no duplicate rows
+ * accumulate when the same (unchanged) template is used repeatedly.
+ *
+ * @property int $id
+ * @property string $slug          Template file slug (filename without extension)
+ * @property int $version          Sequential version number per slug
+ * @property string $name          Template name at snapshot time
+ * @property array $content        Full template content as JSON
+ * @property string $content_hash  SHA-256 of json_encode($content)
+ * @property \Carbon\Carbon|null $created_at
+ * @property \Carbon\Carbon|null $updated_at
+ */
+class PlanTemplateVersion extends Model
+{
+    protected $fillable = [
+        'slug',
+        'version',
+        'name',
+        'content',
+        'content_hash',
+    ];
+
+    protected $casts = [
+        'content' => 'array',
+        'version' => 'integer',
+    ];
+
+    /**
+     * Plans that were created from this template version.
+     */
+    public function plans(): HasMany
+    {
+        return $this->hasMany(AgentPlan::class, 'template_version_id');
+    }
+
+    /**
+     * Find an existing version by content hash, or create a new one.
+     *
+     * Deduplicates identical template content so we don't store redundant rows
+     * when the same (unchanged) template is used multiple times.
+     */
+    public static function findOrCreateFromTemplate(string $slug, array $content): self
+    {
+        $hash = hash('sha256', json_encode($content, JSON_UNESCAPED_UNICODE));
+
+        $existing = static::where('slug', $slug)
+            ->where('content_hash', $hash)
+            ->first();
+
+        if ($existing) {
+            return $existing;
+        }
+
+        $nextVersion = (static::where('slug', $slug)->max('version') ?? 0) + 1;
+
+        return static::create([
+            'slug' => $slug,
+            'version' => $nextVersion,
+            'name' => $content['name'] ?? $slug,
+            'content' => $content,
+            'content_hash' => $hash,
+        ]);
+    }
+
+    /**
+     * Get all recorded versions for a template slug, newest first.
+     *
+     * @return Collection<int, static>
+     */
+    public static function historyFor(string $slug): Collection
+    {
+        return static::where('slug', $slug)
+            ->orderByDesc('version')
+            ->get();
+    }
+}
diff --git a/Services/PlanTemplateService.php b/Services/PlanTemplateService.php
index 9117ea0..3470406 100644
--- a/Services/PlanTemplateService.php
+++ b/Services/PlanTemplateService.php
@@ -6,6 +6,7 @@ namespace Core\Mod\Agentic\Services;
 
 use Core\Mod\Agentic\Models\AgentPhase;
 use Core\Mod\Agentic\Models\AgentPlan;
+use Core\Mod\Agentic\Models\PlanTemplateVersion;
 use Core\Tenant\Models\Workspace;
 use Illuminate\Support\Collection;
 use Illuminate\Support\Facades\File;
@@ -146,6 +147,10 @@ class PlanTemplateService
             return null;
         }
 
+        // Snapshot the raw template content before variable substitution so the
+        // version record captures the canonical template, not the instantiated copy.
+        $templateVersion = PlanTemplateVersion::findOrCreateFromTemplate($templateSlug, $template);
+
         // Replace variables in template
         $template = $this->substituteVariables($template, $variables);
 
@@ -164,10 +169,12 @@ class PlanTemplateService
             'description' => $template['description'] ?? null,
             'context' => $context,
             'status' => ($options['activate'] ?? false) ? AgentPlan::STATUS_ACTIVE : AgentPlan::STATUS_DRAFT,
+            'template_version_id' => $templateVersion->id,
             'metadata' => array_merge($template['metadata'] ?? [], [
                 'source' => 'template',
                 'template_slug' => $templateSlug,
                 'template_name' => $template['name'],
+                'template_version' => $templateVersion->version,
                 'variables' => $variables,
                 'created_at' => now()->toIso8601String(),
             ]),
@@ -361,6 +368,7 @@ class PlanTemplateService
     }
 
     /**
+<<<<<<< HEAD
      * Naming convention reminder included in validation results.
      */
     private const NAMING_CONVENTION = 'Variable names use snake_case (e.g. project_name, api_key)';
@@ -401,6 +409,41 @@ class PlanTemplateService
         return $message;
     }
 
+    /**
+     * Get the version history for a template slug, newest first.
+     *
+     * Returns an array of version summaries (without full content) for display.
+     *
+     * @return array<int, array{id: int, slug: string, version: int, name: string, content_hash: string, created_at: string}>
+     */
+    public function getVersionHistory(string $slug): array
+    {
+        return PlanTemplateVersion::historyFor($slug)
+            ->map(fn (PlanTemplateVersion $v) => [
+                'id' => $v->id,
+                'slug' => $v->slug,
+                'version' => $v->version,
+                'name' => $v->name,
+                'content_hash' => $v->content_hash,
+                'created_at' => $v->created_at?->toIso8601String(),
+            ])
+            ->toArray();
+    }
+
+    /**
+     * Get a specific stored version of a template by slug and version number.
+     *
+     * Returns the snapshotted content array, or null if not found.
+     */
+    public function getVersion(string $slug, int $version): ?array
+    {
+        $record = PlanTemplateVersion::where('slug', $slug)
+            ->where('version', $version)
+            ->first();
+
+        return $record?->content;
+    }
+
     /**
      * Get templates by category.
      */
diff --git a/TODO.md b/TODO.md
index 759ea78..a8daa6c 100644
--- a/TODO.md
+++ b/TODO.md
@@ -191,10 +191,10 @@ Production-quality task list for the AI agent orchestration package.
   - Issue: Archived plans kept forever
   - Fix: Add configurable retention period, cleanup job
 
-- [ ] **FEAT-003: Template version management**
-  - Location: `Services/PlanTemplateService.php`
+- [x] **FEAT-003: Template version management**
+  - Location: `Services/PlanTemplateService.php`, `Models/PlanTemplateVersion.php`
   - Issue: Template changes affect existing plan references
-  - Fix: Add version tracking to templates
+  - Fix: Add version tracking to templates — implemented in #35
 
 ### Consistency
 
diff --git a/tests/Feature/TemplateVersionManagementTest.php b/tests/Feature/TemplateVersionManagementTest.php
new file mode 100644
index 0000000..2fed71e
--- /dev/null
+++ b/tests/Feature/TemplateVersionManagementTest.php
@@ -0,0 +1,320 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Tests for template version management (FEAT-003).
+ *
+ * Covers:
+ * - Version snapshot creation when a plan is created from a template
+ * - Deduplication: identical template content reuses the same version row
+ * - New versions are created when template content changes
+ * - Plans reference their template version
+ * - Version history and retrieval via PlanTemplateService
+ */
+
+use Core\Mod\Agentic\Models\AgentPlan;
+use Core\Mod\Agentic\Models\PlanTemplateVersion;
+use Core\Mod\Agentic\Services\PlanTemplateService;
+use Core\Tenant\Models\Workspace;
+use Illuminate\Support\Facades\File;
+use Symfony\Component\Yaml\Yaml;
+
+// =========================================================================
+// Setup helpers
+// =========================================================================
+
+beforeEach(function () {
+    $this->workspace = Workspace::factory()->create();
+    $this->service = app(PlanTemplateService::class);
+    $this->templatesPath = resource_path('plan-templates');
+
+    if (! File::isDirectory($this->templatesPath)) {
+        File::makeDirectory($this->templatesPath, 0755, true);
+    }
+});
+
+afterEach(function () {
+    if (File::isDirectory($this->templatesPath)) {
+        File::deleteDirectory($this->templatesPath);
+    }
+});
+
+function writeVersionTemplate(string $slug, array $content): void
+{
+    File::put(
+        resource_path('plan-templates').'/'.$slug.'.yaml',
+        Yaml::dump($content, 10)
+    );
+}
+
+// =========================================================================
+// PlanTemplateVersion model
+// =========================================================================
+
+describe('PlanTemplateVersion model', function () {
+    it('creates a new version record on first use', function () {
+        $content = ['name' => 'My Template', 'slug' => 'my-tpl', 'phases' => []];
+
+        $version = PlanTemplateVersion::findOrCreateFromTemplate('my-tpl', $content);
+
+        expect($version)->toBeInstanceOf(PlanTemplateVersion::class)
+            ->and($version->slug)->toBe('my-tpl')
+            ->and($version->version)->toBe(1)
+            ->and($version->name)->toBe('My Template')
+            ->and($version->content)->toBe($content)
+            ->and($version->content_hash)->toBe(hash('sha256', json_encode($content, JSON_UNESCAPED_UNICODE)));
+    });
+
+    it('reuses existing version when content is identical', function () {
+        $content = ['name' => 'Stable', 'slug' => 'stable', 'phases' => []];
+
+        $v1 = PlanTemplateVersion::findOrCreateFromTemplate('stable', $content);
+        $v2 = PlanTemplateVersion::findOrCreateFromTemplate('stable', $content);
+
+        expect($v1->id)->toBe($v2->id)
+            ->and(PlanTemplateVersion::where('slug', 'stable')->count())->toBe(1);
+    });
+
+    it('creates a new version when content changes', function () {
+        $contentV1 = ['name' => 'Template', 'slug' => 'evolving', 'phases' => []];
+        $contentV2 = ['name' => 'Template', 'slug' => 'evolving', 'phases' => [['name' => 'New Phase']]];
+
+        $v1 = PlanTemplateVersion::findOrCreateFromTemplate('evolving', $contentV1);
+        $v2 = PlanTemplateVersion::findOrCreateFromTemplate('evolving', $contentV2);
+
+        expect($v1->id)->not->toBe($v2->id)
+            ->and($v1->version)->toBe(1)
+            ->and($v2->version)->toBe(2)
+            ->and(PlanTemplateVersion::where('slug', 'evolving')->count())->toBe(2);
+    });
+
+    it('increments version numbers sequentially', function () {
+        for ($i = 1; $i <= 3; $i++) {
+            $content = ['name' => "Version {$i}", 'slug' => 'sequential', 'phases' => [$i]];
+            $v = PlanTemplateVersion::findOrCreateFromTemplate('sequential', $content);
+            expect($v->version)->toBe($i);
+        }
+    });
+
+    it('scopes versions by slug independently', function () {
+        $alpha = ['name' => 'Alpha', 'slug' => 'alpha', 'phases' => []];
+        $beta = ['name' => 'Beta', 'slug' => 'beta', 'phases' => []];
+
+        $vA = PlanTemplateVersion::findOrCreateFromTemplate('alpha', $alpha);
+        $vB = PlanTemplateVersion::findOrCreateFromTemplate('beta', $beta);
+
+        expect($vA->version)->toBe(1)
+            ->and($vB->version)->toBe(1)
+            ->and($vA->id)->not->toBe($vB->id);
+    });
+
+    it('returns history for a slug newest first', function () {
+        $content1 = ['name' => 'T', 'slug' => 'hist', 'phases' => [1]];
+        $content2 = ['name' => 'T', 'slug' => 'hist', 'phases' => [2]];
+
+        PlanTemplateVersion::findOrCreateFromTemplate('hist', $content1);
+        PlanTemplateVersion::findOrCreateFromTemplate('hist', $content2);
+
+        $history = PlanTemplateVersion::historyFor('hist');
+
+        expect($history)->toHaveCount(2)
+            ->and($history[0]->version)->toBe(2)
+            ->and($history[1]->version)->toBe(1);
+    });
+
+    it('returns empty collection when no versions exist for slug', function () {
+        $history = PlanTemplateVersion::historyFor('nonexistent-slug');
+
+        expect($history)->toBeEmpty();
+    });
+});
+
+// =========================================================================
+// Plan creation snapshots a template version
+// =========================================================================
+
+describe('plan creation version tracking', function () {
+    it('creates a version record when creating a plan from a template', function () {
+        writeVersionTemplate('versioned-plan', [
+            'name' => 'Versioned Plan',
+            'phases' => [['name' => 'Phase 1']],
+        ]);
+
+        $plan = $this->service->createPlan('versioned-plan', [], [], $this->workspace);
+
+        expect($plan->template_version_id)->not->toBeNull()
+            ->and(PlanTemplateVersion::where('slug', 'versioned-plan')->count())->toBe(1);
+    });
+
+    it('associates the plan with the template version', function () {
+        writeVersionTemplate('linked-version', [
+            'name' => 'Linked Version',
+            'phases' => [],
+        ]);
+
+        $plan = $this->service->createPlan('linked-version', [], [], $this->workspace);
+
+        expect($plan->templateVersion)->toBeInstanceOf(PlanTemplateVersion::class)
+            ->and($plan->templateVersion->slug)->toBe('linked-version')
+            ->and($plan->templateVersion->version)->toBe(1);
+    });
+
+    it('stores template version number in metadata', function () {
+        writeVersionTemplate('meta-version', [
+            'name' => 'Meta Version',
+            'phases' => [],
+        ]);
+
+        $plan = $this->service->createPlan('meta-version', [], [], $this->workspace);
+
+        expect($plan->metadata['template_version'])->toBe(1);
+    });
+
+    it('reuses the same version record for multiple plans from unchanged template', function () {
+        writeVersionTemplate('shared-version', [
+            'name' => 'Shared Template',
+            'phases' => [],
+        ]);
+
+        $plan1 = $this->service->createPlan('shared-version', [], [], $this->workspace);
+        $plan2 = $this->service->createPlan('shared-version', [], [], $this->workspace);
+
+        expect($plan1->template_version_id)->toBe($plan2->template_version_id)
+            ->and(PlanTemplateVersion::where('slug', 'shared-version')->count())->toBe(1);
+    });
+
+    it('creates a new version when template content changes between plan creations', function () {
+        writeVersionTemplate('changing-template', [
+            'name' => 'Original',
+            'phases' => [],
+        ]);
+
+        $plan1 = $this->service->createPlan('changing-template', [], [], $this->workspace);
+
+        // Simulate template file update
+        writeVersionTemplate('changing-template', [
+            'name' => 'Updated',
+            'phases' => [['name' => 'Added Phase']],
+        ]);
+
+        // Re-resolve the service so it reads fresh YAML
+        $freshService = new PlanTemplateService;
+        $plan2 = $freshService->createPlan('changing-template', [], [], $this->workspace);
+
+        expect($plan1->template_version_id)->not->toBe($plan2->template_version_id)
+            ->and($plan1->templateVersion->version)->toBe(1)
+            ->and($plan2->templateVersion->version)->toBe(2)
+            ->and(PlanTemplateVersion::where('slug', 'changing-template')->count())->toBe(2);
+    });
+
+    it('existing plans keep their version reference after template update', function () {
+        writeVersionTemplate('stable-ref', [
+            'name' => 'Stable',
+            'phases' => [],
+        ]);
+
+        $plan = $this->service->createPlan('stable-ref', [], [], $this->workspace);
+        $originalVersionId = $plan->template_version_id;
+
+        // Update template file
+        writeVersionTemplate('stable-ref', [
+            'name' => 'Stable Updated',
+            'phases' => [['name' => 'New Phase']],
+        ]);
+
+        // Reload plan from DB - version reference must be unchanged
+        $plan->refresh();
+
+        expect($plan->template_version_id)->toBe($originalVersionId)
+            ->and($plan->templateVersion->name)->toBe('Stable');
+    });
+
+    it('snapshots raw template content before variable substitution', function () {
+        writeVersionTemplate('raw-snapshot', [
+            'name' => '{{ project }} Plan',
+            'phases' => [['name' => '{{ project }} Setup']],
+        ]);
+
+        $plan = $this->service->createPlan('raw-snapshot', ['project' => 'MyApp'], [], $this->workspace);
+
+        // Version content should retain placeholders, not the substituted values
+        $versionContent = $plan->templateVersion->content;
+
+        expect($versionContent['name'])->toBe('{{ project }} Plan')
+            ->and($versionContent['phases'][0]['name'])->toBe('{{ project }} Setup');
+    });
+});
+
+// =========================================================================
+// PlanTemplateService version methods
+// =========================================================================
+
+describe('PlanTemplateService version methods', function () {
+    it('getVersionHistory returns empty array when no plans created', function () {
+        $history = $this->service->getVersionHistory('no-plans-yet');
+
+        expect($history)->toBeArray()->toBeEmpty();
+    });
+
+    it('getVersionHistory returns version summaries after plan creation', function () {
+        writeVersionTemplate('hist-service', [
+            'name' => 'History Template',
+            'phases' => [],
+        ]);
+
+        $this->service->createPlan('hist-service', [], [], $this->workspace);
+
+        $history = $this->service->getVersionHistory('hist-service');
+
+        expect($history)->toHaveCount(1)
+            ->and($history[0])->toHaveKeys(['id', 'slug', 'version', 'name', 'content_hash', 'created_at'])
+            ->and($history[0]['slug'])->toBe('hist-service')
+            ->and($history[0]['version'])->toBe(1)
+            ->and($history[0]['name'])->toBe('History Template');
+    });
+
+    it('getVersionHistory orders newest version first', function () {
+        writeVersionTemplate('order-hist', ['name' => 'V1', 'phases' => []]);
+        $this->service->createPlan('order-hist', [], [], $this->workspace);
+
+        writeVersionTemplate('order-hist', ['name' => 'V2', 'phases' => [['name' => 'p']]]);
+        $freshService = new PlanTemplateService;
+        $freshService->createPlan('order-hist', [], [], $this->workspace);
+
+        $history = $this->service->getVersionHistory('order-hist');
+
+        expect($history[0]['version'])->toBe(2)
+            ->and($history[1]['version'])->toBe(1);
+    });
+
+    it('getVersion returns content for an existing version', function () {
+        $templateContent = ['name' => 'Get Version Test', 'phases' => []];
+        writeVersionTemplate('get-version', $templateContent);
+
+        $this->service->createPlan('get-version', [], [], $this->workspace);
+
+        $content = $this->service->getVersion('get-version', 1);
+
+        expect($content)->not->toBeNull()
+            ->and($content['name'])->toBe('Get Version Test');
+    });
+
+    it('getVersion returns null for nonexistent version', function () {
+        $content = $this->service->getVersion('nonexistent', 99);
+
+        expect($content)->toBeNull();
+    });
+
+    it('getVersion returns the correct historic content when template has changed', function () {
+        writeVersionTemplate('historic-content', ['name' => 'Original Name', 'phases' => []]);
+        $this->service->createPlan('historic-content', [], [], $this->workspace);
+
+        writeVersionTemplate('historic-content', ['name' => 'Updated Name', 'phases' => [['name' => 'p']]]);
+        $freshService = new PlanTemplateService;
+        $freshService->createPlan('historic-content', [], [], $this->workspace);
+
+        expect($this->service->getVersion('historic-content', 1)['name'])->toBe('Original Name')
+            ->and($this->service->getVersion('historic-content', 2)['name'])->toBe('Updated Name');
+    });
+});