diff --git a/Concerns/LogsWorkspaceActivity.php b/Concerns/LogsWorkspaceActivity.php
new file mode 100644
index 0000000..416adff
--- /dev/null
+++ b/Concerns/LogsWorkspaceActivity.php
@@ -0,0 +1,136 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Core\Tenant\Concerns;
+
+use Core\Tenant\Models\User;
+use Core\Tenant\Models\Workspace;
+use Core\Tenant\Models\WorkspaceActivity;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * Trait for models that should log workspace activity on changes.
+ *
+ * Usage:
+ *   class WorkspaceMember extends Model {
+ *       use LogsWorkspaceActivity;
+ *
+ *       protected static string $activityActionPrefix = 'member';
+ *   }
+ *
+ * For auto-logging create/update/delete:
+ *   class WorkspaceMember extends Model {
+ *       use LogsWorkspaceActivity;
+ *
+ *       protected static bool $autoLogActivity = true;
+ *       protected static string $activityActionPrefix = 'member';
+ *   }
+ *
+ * For manual logging:
+ *   $model->logActivity('member.role_changed', ['old_role' => 'member', 'new_role' => 'admin']);
+ */
+trait LogsWorkspaceActivity
+{
+    /**
+     * Boot the trait — optionally auto-log on create/update/delete.
+     */
+    protected static function bootLogsWorkspaceActivity(): void
+    {
+        if (static::shouldAutoLog()) {
+            static::created(function (Model $model) {
+                $model->logActivityIfWorkspaced('created');
+            });
+
+            static::updated(function (Model $model) {
+                $model->logActivityIfWorkspaced('updated', [
+                    'changed' => $model->getChanges(),
+                ]);
+            });
+
+            static::deleted(function (Model $model) {
+                $model->logActivityIfWorkspaced('deleted');
+            });
+        }
+    }
+
+    /**
+     * Whether this model should auto-log create/update/delete events.
+     *
+     * Override in model to enable: protected static bool $autoLogActivity = true;
+     */
+    protected static function shouldAutoLog(): bool
+    {
+        return property_exists(static::class, 'autoLogActivity')
+            && static::$autoLogActivity === true;
+    }
+
+    /**
+     * Log an activity for this model within its workspace context.
+     */
+    public function logActivity(string $action, ?array $metadata = null, ?User $user = null): WorkspaceActivity
+    {
+        $workspaceId = $this->getActivityWorkspaceId();
+
+        return WorkspaceActivity::record(
+            workspace: $workspaceId,
+            action: $action,
+            subject: $this,
+            user: $user,
+            metadata: $metadata,
+        );
+    }
+
+    /**
+     * Log activity only if the model has a workspace context.
+     */
+    protected function logActivityIfWorkspaced(string $suffix, ?array $metadata = null): void
+    {
+        $workspaceId = $this->getActivityWorkspaceId();
+
+        if ($workspaceId === null) {
+            return;
+        }
+
+        $action = static::getActivityActionPrefix() . '.' . $suffix;
+
+        WorkspaceActivity::record(
+            workspace: $workspaceId,
+            action: $action,
+            subject: $this,
+            metadata: $metadata,
+        );
+    }
+
+    /**
+     * Get the workspace ID for this model's activity log.
+     *
+     * Override in model if the workspace relationship differs.
+     */
+    protected function getActivityWorkspaceId(): ?int
+    {
+        if (property_exists($this, 'workspace_id') || $this->getAttribute('workspace_id')) {
+            return $this->getAttribute('workspace_id');
+        }
+
+        // Try to resolve from the current workspace context
+        $workspace = Workspace::current();
+
+        return $workspace?->id;
+    }
+
+    /**
+     * Get the action prefix for auto-logged events.
+     *
+     * Override via: protected static string $activityActionPrefix = 'custom_prefix';
+     */
+    protected static function getActivityActionPrefix(): string
+    {
+        if (property_exists(static::class, 'activityActionPrefix')) {
+            return static::$activityActionPrefix;
+        }
+
+        // Derive from class name: WorkspaceMember -> workspace_member
+        return strtolower((string) preg_replace('/(?<!^)[A-Z]/', '_$0', class_basename(static::class)));
+    }
+}
diff --git a/Migrations/2026_03_24_000000_create_workspace_activities_table.php b/Migrations/2026_03_24_000000_create_workspace_activities_table.php
new file mode 100644
index 0000000..1b1df1f
--- /dev/null
+++ b/Migrations/2026_03_24_000000_create_workspace_activities_table.php
@@ -0,0 +1,36 @@
+<?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
+{
+    /**
+     * Workspace activity audit log for tracking significant workspace actions.
+     */
+    public function up(): void
+    {
+        Schema::create('workspace_activities', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('workspace_id')->constrained()->cascadeOnDelete();
+            $table->foreignId('user_id')->nullable()->constrained()->nullOnDelete();
+            $table->string('action');
+            $table->nullableMorphs('subject');
+            $table->json('metadata')->nullable();
+            $table->timestamp('created_at')->nullable();
+
+            $table->index(['workspace_id', 'action'], 'ws_activity_ws_action_idx');
+            $table->index(['workspace_id', 'created_at'], 'ws_activity_ws_created_idx');
+            $table->index(['subject_type', 'subject_id'], 'ws_activity_subject_idx');
+            $table->index('user_id', 'ws_activity_user_idx');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('workspace_activities');
+    }
+};
diff --git a/Models/Workspace.php b/Models/Workspace.php
index 490bc64..09d5ed8 100644
--- a/Models/Workspace.php
+++ b/Models/Workspace.php
@@ -250,6 +250,14 @@ class Workspace extends Model
         return $this->hasMany(EntitlementLog::class);
     }
 
+    /**
+     * Activity audit log for this workspace.
+     */
+    public function activities(): HasMany
+    {
+        return $this->hasMany(WorkspaceActivity::class);
+    }
+
     /**
      * Usage alert history for this workspace.
      */
diff --git a/Models/WorkspaceActivity.php b/Models/WorkspaceActivity.php
new file mode 100644
index 0000000..bdee318
--- /dev/null
+++ b/Models/WorkspaceActivity.php
@@ -0,0 +1,256 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Core\Tenant\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+/**
+ * Workspace Activity - audit log for significant workspace actions.
+ *
+ * Tracks security events, membership changes, entitlement changes, and
+ * other significant actions within a workspace.
+ *
+ * @property int $id
+ * @property int $workspace_id
+ * @property int|null $user_id
+ * @property string $action
+ * @property string|null $subject_type
+ * @property int|null $subject_id
+ * @property array|null $metadata
+ * @property \Carbon\Carbon|null $created_at
+ */
+class WorkspaceActivity extends Model
+{
+    /**
+     * Disable updated_at since this is an append-only audit log.
+     */
+    public const UPDATED_AT = null;
+
+    protected $table = 'workspace_activities';
+
+    protected $fillable = [
+        'workspace_id',
+        'user_id',
+        'action',
+        'subject_type',
+        'subject_id',
+        'metadata',
+    ];
+
+    protected $casts = [
+        'metadata' => 'array',
+    ];
+
+    // ─────────────────────────────────────────────────────────────────────────
+    // Action Constants — Workspace
+    // ─────────────────────────────────────────────────────────────────────────
+
+    public const ACTION_WORKSPACE_CREATED = 'workspace.created';
+
+    public const ACTION_WORKSPACE_UPDATED = 'workspace.updated';
+
+    public const ACTION_WORKSPACE_DELETED = 'workspace.deleted';
+
+    public const ACTION_WORKSPACE_SETTINGS_CHANGED = 'workspace.settings_changed';
+
+    // ─────────────────────────────────────────────────────────────────────────
+    // Action Constants — Membership
+    // ─────────────────────────────────────────────────────────────────────────
+
+    public const ACTION_MEMBER_INVITED = 'member.invited';
+
+    public const ACTION_MEMBER_JOINED = 'member.joined';
+
+    public const ACTION_MEMBER_REMOVED = 'member.removed';
+
+    public const ACTION_MEMBER_ROLE_CHANGED = 'member.role_changed';
+
+    public const ACTION_MEMBER_TEAM_CHANGED = 'member.team_changed';
+
+    // ─────────────────────────────────────────────────────────────────────────
+    // Action Constants — Entitlements
+    // ─────────────────────────────────────────────────────────────────────────
+
+    public const ACTION_PACKAGE_ASSIGNED = 'package.assigned';
+
+    public const ACTION_PACKAGE_REMOVED = 'package.removed';
+
+    public const ACTION_BOOST_APPLIED = 'boost.applied';
+
+    public const ACTION_BOOST_REMOVED = 'boost.removed';
+
+    // ─────────────────────────────────────────────────────────────────────────
+    // Action Constants — Security Events
+    // ─────────────────────────────────────────────────────────────────────────
+
+    public const ACTION_API_KEY_CREATED = 'api_key.created';
+
+    public const ACTION_API_KEY_REVOKED = 'api_key.revoked';
+
+    public const ACTION_WEBHOOK_CREATED = 'webhook.created';
+
+    public const ACTION_WEBHOOK_DELETED = 'webhook.deleted';
+
+    // ─────────────────────────────────────────────────────────────────────────
+    // Relationships
+    // ─────────────────────────────────────────────────────────────────────────
+
+    /**
+     * The workspace this activity belongs to.
+     */
+    public function workspace(): BelongsTo
+    {
+        return $this->belongsTo(Workspace::class);
+    }
+
+    /**
+     * The user who performed this action.
+     */
+    public function user(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    /**
+     * The subject (polymorphic) of this activity.
+     */
+    public function subject(): MorphTo
+    {
+        return $this->morphTo();
+    }
+
+    // ─────────────────────────────────────────────────────────────────────────
+    // Scopes
+    // ─────────────────────────────────────────────────────────────────────────
+
+    /**
+     * Scope to a specific workspace.
+     */
+    public function scopeForWorkspace($query, Workspace|int $workspace)
+    {
+        $workspaceId = $workspace instanceof Workspace ? $workspace->id : $workspace;
+
+        return $query->where('workspace_id', $workspaceId);
+    }
+
+    /**
+     * Scope to a specific action.
+     */
+    public function scopeForAction($query, string $action)
+    {
+        return $query->where('action', $action);
+    }
+
+    /**
+     * Scope to a specific action prefix (e.g. 'member.' matches all member actions).
+     */
+    public function scopeForActionGroup($query, string $prefix)
+    {
+        return $query->where('action', 'like', $prefix . '%');
+    }
+
+    /**
+     * Scope to a specific subject.
+     */
+    public function scopeForSubject($query, Model $subject)
+    {
+        return $query
+            ->where('subject_type', $subject->getMorphClass())
+            ->where('subject_id', $subject->getKey());
+    }
+
+    /**
+     * Scope to a specific user.
+     */
+    public function scopeByUser($query, User|int $user)
+    {
+        $userId = $user instanceof User ? $user->id : $user;
+
+        return $query->where('user_id', $userId);
+    }
+
+    /**
+     * Scope to activities within a date range.
+     */
+    public function scopeBetween($query, $from, $to)
+    {
+        return $query->whereBetween('created_at', [$from, $to]);
+    }
+
+    /**
+     * Order by most recent first.
+     */
+    public function scopeLatestFirst($query)
+    {
+        return $query->orderByDesc('created_at');
+    }
+
+    // ─────────────────────────────────────────────────────────────────────────
+    // Factory Methods
+    // ─────────────────────────────────────────────────────────────────────────
+
+    /**
+     * Record a workspace activity.
+     */
+    public static function record(
+        Workspace|int $workspace,
+        string $action,
+        ?Model $subject = null,
+        ?User $user = null,
+        ?array $metadata = null,
+    ): self {
+        $workspaceId = $workspace instanceof Workspace ? $workspace->id : $workspace;
+
+        return self::create([
+            'workspace_id' => $workspaceId,
+            'user_id' => $user?->id ?? auth()->id(),
+            'action' => $action,
+            'subject_type' => $subject?->getMorphClass(),
+            'subject_id' => $subject?->getKey(),
+            'metadata' => $metadata,
+        ]);
+    }
+
+    /**
+     * Record a membership change.
+     */
+    public static function recordMembershipChange(
+        Workspace|int $workspace,
+        string $action,
+        WorkspaceMember|User $subject,
+        ?User $performedBy = null,
+        ?array $metadata = null,
+    ): self {
+        return self::record($workspace, $action, $subject, $performedBy, $metadata);
+    }
+
+    /**
+     * Record an entitlement change.
+     */
+    public static function recordEntitlementChange(
+        Workspace|int $workspace,
+        string $action,
+        Model $subject,
+        ?User $performedBy = null,
+        ?array $metadata = null,
+    ): self {
+        return self::record($workspace, $action, $subject, $performedBy, $metadata);
+    }
+
+    /**
+     * Record a security event.
+     */
+    public static function recordSecurityEvent(
+        Workspace|int $workspace,
+        string $action,
+        ?Model $subject = null,
+        ?User $performedBy = null,
+        ?array $metadata = null,
+    ): self {
+        return self::record($workspace, $action, $subject, $performedBy, $metadata);
+    }
+}