diff --git a/src/Entity/Task.php b/src/Entity/Task.php
index 320468f..639b929 100644
--- a/src/Entity/Task.php
+++ b/src/Entity/Task.php
@@ -38,7 +38,7 @@ use Symfony\Component\Validator\Context\ExecutionContextInterface;
     denormalizationContext: ['groups' => ['task:write']],
     order: ['id' => 'DESC'],
 )]
-#[ApiFilter(SearchFilter::class, properties: ['project' => 'exact', 'group' => 'exact', 'assignee' => 'exact', 'priority' => 'exact', 'effort' => 'exact', 'tags' => 'exact', 'status' => 'exact'])]
+#[ApiFilter(SearchFilter::class, properties: ['project' => 'exact', 'group' => 'exact', 'assignee' => 'exact', 'collaborators' => 'exact', 'priority' => 'exact', 'effort' => 'exact', 'tags' => 'exact', 'status' => 'exact'])]
 #[ApiFilter(DateFilter::class, properties: ['scheduledStart', 'scheduledEnd', 'deadline'])]
 #[ApiFilter(BooleanFilter::class, properties: ['archived', 'syncToCalendar'])]
 #[ApiFilter(OrderFilter::class, properties: ['scheduledStart', 'deadline'])]
@@ -85,6 +85,16 @@ class Task
     #[Groups(['task:read', 'task:write'])]
     private ?User $assignee = null;
 
+    /** @var Collection<int, User> */
+    #[ORM\ManyToMany(targetEntity: User::class)]
+    #[ORM\JoinTable(
+        name: 'task_collaborator',
+        joinColumns: [new ORM\JoinColumn(name: 'task_id', referencedColumnName: 'id', onDelete: 'CASCADE')],
+        inverseJoinColumns: [new ORM\JoinColumn(name: 'user_id', referencedColumnName: 'id', onDelete: 'CASCADE')],
+    )]
+    #[Groups(['task:read', 'task:write'])]
+    private Collection $collaborators;
+
     #[ORM\ManyToOne(targetEntity: TaskGroup::class)]
     #[ORM\JoinColumn(nullable: true, onDelete: 'SET NULL')]
     #[Groups(['task:read', 'task:write'])]
@@ -152,8 +162,9 @@ class Task
 
     public function __construct()
     {
-        $this->tags      = new ArrayCollection();
-        $this->documents = new ArrayCollection();
+        $this->tags          = new ArrayCollection();
+        $this->documents     = new ArrayCollection();
+        $this->collaborators = new ArrayCollection();
     }
 
     public function getId(): ?int
@@ -245,6 +256,28 @@ class Task
         return $this;
     }
 
+    /** @return Collection<int, User> */
+    public function getCollaborators(): Collection
+    {
+        return $this->collaborators;
+    }
+
+    public function addCollaborator(User $user): static
+    {
+        if (!$this->collaborators->contains($user)) {
+            $this->collaborators->add($user);
+        }
+
+        return $this;
+    }
+
+    public function removeCollaborator(User $user): static
+    {
+        $this->collaborators->removeElement($user);
+
+        return $this;
+    }
+
     public function getGroup(): ?TaskGroup
     {
         return $this->group;
@@ -434,4 +467,15 @@ class Task
             ;
         }
     }
+
+    #[Assert\Callback]
+    public function validateCollaborators(ExecutionContextInterface $context): void
+    {
+        if (null !== $this->assignee && $this->collaborators->contains($this->assignee)) {
+            $context->buildViolation('The assignee cannot also be a collaborator.')
+                ->atPath('collaborators')
+                ->addViolation()
+            ;
+        }
+    }
 }