diff --git a/composer.json b/composer.json
index d9c7a51db..175fbc512 100644
--- a/composer.json
+++ b/composer.json
@@ -98,7 +98,7 @@
     "require-dev": {
         "doctrine/doctrine-fixtures-bundle": "^3.3",
         "fakerphp/faker": "^1.13",
-        "friendsofphp/php-cs-fixer": "3.93.0",
+        "friendsofphp/php-cs-fixer": "^3.94",
         "jangregor/phpstan-prophecy": "^1.0",
         "nelmio/alice": "^3.8",
         "nikic/php-parser": "^4.15",
@@ -113,13 +113,13 @@
         "symfony/debug-bundle": "^5.4",
         "symfony/dotenv": "^5.4",
         "symfony/flex": "^2.4",
+        "symfony/loco-translation-provider": "^6.0",
         "symfony/maker-bundle": "^1.20",
         "symfony/phpunit-bridge": "^7.1",
         "symfony/runtime": "^5.4",
         "symfony/stopwatch": "^5.4",
         "symfony/var-dumper": "^5.4",
-        "symfony/web-profiler-bundle": "^5.4",
-        "symfony/loco-translation-provider": "^6.0"
+        "symfony/web-profiler-bundle": "^5.4"
     },
     "conflict": {
         "symfony/symfony": "*"
diff --git a/package.json b/package.json
index 12a5fee26..cd4f23a07 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
     "@hotwired/stimulus": "^3.0.0",
     "@luminateone/eslint-baseline": "^1.0.9",
     "@symfony/stimulus-bridge": "^3.2.0",
+    "@symfony/ux-translator": "file:vendor/symfony/ux-translator/assets",
     "@symfony/webpack-encore": "^4.1.0",
     "@tsconfig/node20": "^20.1.4",
     "@types/dompurify": "^3.0.5",
diff --git a/src/Bundle/ChillPersonBundle/Entity/Person/Upsert/Handler/PersonUpsertHandler.php b/src/Bundle/ChillPersonBundle/Entity/Person/Upsert/Handler/PersonUpsertHandler.php
new file mode 100644
index 000000000..e5ab106e7
--- /dev/null
+++ b/src/Bundle/ChillPersonBundle/Entity/Person/Upsert/Handler/PersonUpsertHandler.php
@@ -0,0 +1,83 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace Chill\Bundle\ChillPersonBundle\Entity\Person\Upsert\Handler;
+
+use Chill\PersonBundle\Repository\PersonRepository;
+use Chill\PersonBundle\Repository\Identifier\PersonIdentifierDefinitionRepository;
+use Chill\PersonBundle\Repository\Identifier\PersonIdentifierRepository;
+use Chill\PersonBundle\Entity\Person;
+use Chill\PersonBundle\Entity\Identifier\PersonIdentifier;
+use Chill\PersonBundle\Entity\Person\Upsert\UpsertMessage;
+use Symfony\Component\Messenger\Attribute\AsMessageHandler;
+use Doctrine\ORM\EntityManagerInterface;
+
+#[AsMessageHandler]
+class PersonUpsertHandler
+{
+    public function __construct(
+        // TODO: Utiliser findByExternalId à la place de findByDefinitionAndCanonical ?
+        private readonly PersonRepository $personRepository,
+        private readonly PersonIdentifierDefinitionRepository $personIdentifierDefinitionRepository,
+        private readonly PersonIdentifierRepository $personIdentifierRepository,
+        private readonly EntityManagerInterface $entityManager,
+    ) {}
+
+    public function __invoke(UpsertMessage $message): void
+    {
+        // 1. Récupérer la définition
+        $definition = $this->personIdentifierDefinitionRepository->find($message->personIdentifierDefinitionId);
+        if (!$definition) {
+            throw new \RuntimeException('PersonIdentifierDefinition non trouvée pour l\'id '.$message->personIdentifierDefinitionId);
+        }
+
+        // 2. Chercher les identifiants
+        $identifiers = $this->personIdentifierRepository->findByDefinitionAndCanonical($definition, $message->externalId);
+
+        if (count($identifiers) > 1) {
+            throw new \RuntimeException('Plus d\'un identifiant trouvé pour la définition et la valeur donnée.');
+        }
+
+        if (0 === count($identifiers)) {
+            // 3. Créer une nouvelle entité Person
+            $person = new Person();
+            if (null !== $message->firstName) {
+                $person->setFirstName($message->firstName);
+            }
+            if (null !== $message->lastName) {
+                $person->setLastName($message->lastName);
+            }
+            $this->entityManager->persist($person);
+
+            // Créer l'identifiant et l'associer
+            $identifier = new PersonIdentifier($definition);
+            $identifier->setPerson($person);
+            $identifier->setValue(['content' => $message->externalId]);
+            $this->entityManager->persist($identifier);
+        } else {
+            // 4. Mettre à jour le Person existant
+            /** @var PersonIdentifier $identifier */
+            $identifier = $identifiers[0];
+            $person = $identifier->getPerson();
+            if (null === $person) {
+                throw new \RuntimeException('L\'identifiant trouvé n\'est lié à aucun Person.');
+            }
+            if (null !== $message->firstName) {
+                $person->setFirstName($message->firstName);
+            }
+            if (null !== $message->lastName) {
+                $person->setLastName($message->lastName);
+            }
+        }
+
+        $this->entityManager->flush();
+    }
+}
diff --git a/src/Bundle/ChillPersonBundle/Entity/Person/Upsert/UpsertMessage.php b/src/Bundle/ChillPersonBundle/Entity/Person/Upsert/UpsertMessage.php
new file mode 100644
index 000000000..81e9d6eb2
--- /dev/null
+++ b/src/Bundle/ChillPersonBundle/Entity/Person/Upsert/UpsertMessage.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace Chill\PersonBundle\Entity\Person\Upsert;
+
+class UpsertMessage
+{
+    public string $externalId;
+    public int $personIdentifierDefinitionId;
+    public ?string $firstName = null;
+    public ?string $lastName = null;
+}
diff --git a/src/Bundle/ChillPersonBundle/Repository/PersonRepository.php b/src/Bundle/ChillPersonBundle/Repository/PersonRepository.php
index 8d5e244ea..d0db5fbcc 100644
--- a/src/Bundle/ChillPersonBundle/Repository/PersonRepository.php
+++ b/src/Bundle/ChillPersonBundle/Repository/PersonRepository.php
@@ -73,6 +73,11 @@ class PersonRepository implements ObjectRepository
         return $this->repository->findBy(['id' => $ids]);
     }
 
+    public function findByExternalId(string $externalId): ?Person
+    {
+        return $this->repository->findOneBy(['externalId' => $externalId]);
+    }
+
     /**
      * @throws \Exception
      *