diff --git a/lemarche/templates/layouts/base.html b/lemarche/templates/layouts/base.html
index 25e8297a4..6b5d8af6b 100644
--- a/lemarche/templates/layouts/base.html
+++ b/lemarche/templates/layouts/base.html
@@ -51,7 +51,7 @@
     {% block extra_head %}{% endblock %}
 </head>
 
-<body id="top" class="{% block body_class %}{% endblock %}">
+<body id="top" class="{% block body_class %}{% endblock %}" hx-headers='{"X-CSRFToken": "{{ csrf_token }}"}'>
     <!-- allow a user to go to the main content of the page -->
     <noscript>
         <div class="alert alert-danger" role="status">
diff --git a/lemarche/templates/tenders/_detail_cocontracting_click_confirm.html b/lemarche/templates/tenders/_detail_cocontracting_click_confirm.html
new file mode 100644
index 000000000..e7fbcba4f
--- /dev/null
+++ b/lemarche/templates/tenders/_detail_cocontracting_click_confirm.html
@@ -0,0 +1,6 @@
+<div class="alert alert-success mt-3 mt-lg-0" role="alert">
+    <p class="mb-0 fs-sm">
+        Nous avons bien pris en compte votre demande de mise en relation.
+        Notre équipe revient vers vous dans les plus brefs délais.
+    </p>
+</div>
diff --git a/lemarche/templates/tenders/_detail_cocontracting_click_error.html b/lemarche/templates/tenders/_detail_cocontracting_click_error.html
new file mode 100644
index 000000000..9e6b60975
--- /dev/null
+++ b/lemarche/templates/tenders/_detail_cocontracting_click_error.html
@@ -0,0 +1,5 @@
+<div class="alert alert-danger mt-3 mt-lg-0" role="alert">
+    <p class="mb-0 fs-sm">
+        N'ayant pu identifier votre structure, nous n'avons pas pu prendre en compte votre demande de mise en relation.
+    </p>
+</div>
diff --git a/lemarche/templates/tenders/_detail_cta_cocontracting.html b/lemarche/templates/tenders/_detail_cta_cocontracting.html
new file mode 100644
index 000000000..af7d92e7d
--- /dev/null
+++ b/lemarche/templates/tenders/_detail_cta_cocontracting.html
@@ -0,0 +1,17 @@
+<div id="detail_cocontracting_container" class="mt-3">
+    <div class="card c-card rounded-lg shadow-lg">
+        <div class="card-body">
+            <h3>Répondre en co-traitance ?</h3>
+            <p>Notre équipe vous met en relation avec d’autres structures désireuses de répondre en co-traitance.</p>
+            {% if user.is_authenticated %}
+                <button type="button" class="btn btn-primary btn-block" title="Être mis en relation" hx-post="{% url 'tenders:detail-cocontracting-click' tender.slug %}" hx-target="#detail_cocontracting_container">
+                    Être mis en relation
+                </button>
+            {% elif siae_id %}
+                <button type="button" class="btn btn-primary btn-block" title="Être mis en relation" hx-post="{% url 'tenders:detail-cocontracting-click' tender.slug %}?siae_id={{siae_id}}" hx-target="#detail_cocontracting_container">
+                    Être mis en relation
+                </button>
+            {% endif %}
+        </div>
+    </div>
+</div>
diff --git a/lemarche/templates/tenders/cocontracting_notification_email_admin_body.txt b/lemarche/templates/tenders/cocontracting_notification_email_admin_body.txt
new file mode 100644
index 000000000..278c3b98f
--- /dev/null
+++ b/lemarche/templates/tenders/cocontracting_notification_email_admin_body.txt
@@ -0,0 +1,8 @@
+La structure {{ siae_name|safe }} souhaite répondre en co-traitance
+
+Titre : {{ tender_title|safe }}
+Type : {{ tender_kind|safe }}
+Contact email de l'ESI: {{ siae_contact_email|safe }}
+SIRET : {{ siae_siret|safe }}
+
+Lien dans l'admin : {{ tender_admin_url }}
diff --git a/lemarche/templates/tenders/detail.html b/lemarche/templates/tenders/detail.html
index 927bdf45d..7187fbcb1 100644
--- a/lemarche/templates/tenders/detail.html
+++ b/lemarche/templates/tenders/detail.html
@@ -148,11 +148,13 @@
                                     </div>
                                 {% elif not user_siae_has_detail_contact_click_date %}
                                     {% include "tenders/_detail_cta.html" with tender=tender user_can_click=True %}
+                                    {% include "tenders/_detail_cta_cocontracting.html" with tender=tender %}
                                 {% endif %}
                             {% endif %}
                         {% elif siae_id %}
                             {% if not siae_has_detail_contact_click_date %}
                                 {% include "tenders/_detail_cta.html" with tender=tender user_can_click=True siae_id=siae_id %}
+                                {% include "tenders/_detail_cta_cocontracting.html" with tender=tender siae_id=siae_id %}
                             {% else %}
                                 {% include "tenders/_detail_contact.html" with tender=tender %}
                             {% endif %}
diff --git a/lemarche/www/tenders/tasks.py b/lemarche/www/tenders/tasks.py
index a3cd7445c..473540845 100644
--- a/lemarche/www/tenders/tasks.py
+++ b/lemarche/www/tenders/tasks.py
@@ -533,3 +533,27 @@ def send_tenders_author_30_days(tender: Tender, kind="feedback"):
         }
         tender.logs.append(log_item)
         tender.save()
+
+
+def notify_admin_siae_wants_cocontracting(tender: Tender, siae: Siae):
+    email_subject = f"Marché de l'inclusion : la structure {siae.name} souhaite répondre en co-traitance"
+    tender_admin_url = get_admin_url_object(tender)
+    email_body = render_to_string(
+        "tenders/cocontracting_notification_email_admin_body.txt",
+        {
+            "tender_title": tender.title,
+            "tender_kind": tender.get_kind_display(),
+            "tender_admin_url": tender_admin_url,
+            "siae_name": siae.name,
+            "siae_contact_email": siae.contact_email,
+            "siae_siret": siae.siret,
+        },
+    )
+    send_mail_async(
+        email_subject=email_subject,
+        email_body=email_body,
+        recipient_list=[settings.NOTIFY_EMAIL],
+    )
+
+    if settings.BITOUBI_ENV == "prod":
+        api_slack.send_message_to_channel(text=email_body, service_id=settings.SLACK_WEBHOOK_C4_SUPPORT_CHANNEL)
diff --git a/lemarche/www/tenders/tests.py b/lemarche/www/tenders/tests.py
index bdd6598c2..844aa60a1 100644
--- a/lemarche/www/tenders/tests.py
+++ b/lemarche/www/tenders/tests.py
@@ -1,5 +1,6 @@
 import json
 from datetime import timedelta
+from unittest import mock
 
 from django.conf import settings
 from django.contrib.gis.geos import Point
@@ -849,8 +850,44 @@ def test_tender_contact_details_display(self):
         self.assertNotContains(response, "Voir l'appel d'offres")
         self.assertContains(response, "Lien partagé")
 
+    def test_tender_cocontracting_display(self):
+        # anonymous
+        url = reverse("tenders:detail", kwargs={"slug": self.tender_1.slug})
+        response = self.client.get(url)
+        self.assertNotContains(response, "Répondre en co-traitance ?")
+        # anonymous but with siae_id in url
+        url = reverse("tenders:detail", kwargs={"slug": self.tender_1.slug})
+        response = self.client.get(f"{url}?siae_id=15")
+        self.assertContains(response, "Répondre en co-traitance ?")
+        # siae user interested but has a detail_contact_click_date
+        self.client.force_login(self.siae_user_1)
+        url = reverse("tenders:detail", kwargs={"slug": self.tender_1.slug})
+        response = self.client.get(url)
+        self.assertNotContains(response, "Répondre en co-traitance ?")
+        # siae user not concerned
+        self.client.force_login(self.siae_user_2)
+        url = reverse("tenders:detail", kwargs={"slug": self.tender_1.slug})
+        response = self.client.get(url)
+        self.assertContains(response, "Répondre en co-traitance ?")
+        # siae user interested
+        TenderSiae.objects.create(tender=self.tender_1, siae=self.siae_2, email_send_date=timezone.now())
+        self.client.force_login(self.siae_user_2)
+        url = reverse("tenders:detail", kwargs={"slug": self.tender_1.slug})
+        response = self.client.get(url)
+        self.assertContains(response, "Répondre en co-traitance ?")
+        # siae user without siae
+        self.client.force_login(self.siae_user_3)
+        url = reverse("tenders:detail", kwargs={"slug": self.tender_1.slug})
+        response = self.client.get(url)
+        self.assertNotContains(response, "Répondre en co-traitance ?")
+        # author
+        self.client.force_login(self.user_buyer_1)
+        url = reverse("tenders:detail", kwargs={"slug": self.tender_1.slug})
+        response = self.client.get(url)
+        self.assertNotContains(response, "Répondre en co-traitance ?")
 
-class TenderDetailContactClickStatViewViewTest(TestCase):
+
+class TenderDetailContactClickStatViewTest(TestCase):
     @classmethod
     def setUpTestData(cls):
         cls.siae = SiaeFactory(name="ZZ ESI")
@@ -962,6 +999,65 @@ def test_update_tendersiae_stats_on_tender_contact_click_with_siae_id_param(self
         )
 
 
+class TenderDetailCocontractingClickView(TestCase):
+    @classmethod
+    def setUpTestData(self):
+        self.siae = SiaeFactory(name="ZZ ESI")
+        self.siae_user = UserFactory(kind=User.KIND_SIAE, siaes=[self.siae])
+        self.user_buyer = UserFactory(kind=User.KIND_BUYER, company_name="Entreprise Buyer")
+        self.tender = TenderFactory(
+            kind=tender_constants.KIND_TENDER,
+            author=self.user_buyer,
+            amount=tender_constants.AMOUNT_RANGE_100_150,
+            accept_share_amount=True,
+            response_kind=[Tender.RESPONSE_KIND_EMAIL],
+        )
+        self.tendersiae = TenderSiae.objects.create(
+            tender=self.tender,
+            siae=self.siae,
+            source="EMAIL",
+            email_send_date=timezone.now(),
+            email_link_click_date=timezone.now(),
+            detail_display_date=timezone.now(),
+            detail_contact_click_date=timezone.now(),
+        )
+        TenderQuestionFactory(tender=self.tender)
+
+    def test_user_can_notify_cocontracting_wish(self):
+        url = reverse("tenders:detail-cocontracting-click", kwargs={"slug": self.tender.slug})
+        with mock.patch("lemarche.www.tenders.tasks.send_mail_async") as mock_send_mail_async:
+            response = self.client.post(url, data={})
+        self.assertEqual(response.status_code, 403)
+        mock_send_mail_async.assert_not_called()
+
+        with mock.patch("lemarche.www.tenders.tasks.send_mail_async") as mock_send_mail_async:
+            response = self.client.post(f"{url}?siae_id=999999", data={})
+        self.assertContains(response, "nous n'avons pas pu prendre en compte votre demande de mise en relation")
+        mock_send_mail_async.assert_not_called()
+
+        with mock.patch("lemarche.www.tenders.tasks.send_mail_async") as mock_send_mail_async:
+            response = self.client.post(f"{url}?siae_id={self.siae.id}", data={})
+        self.assertContains(response, "Nous avons bien pris en compte votre demande de mise en relation")
+        mock_send_mail_async.assert_called_once()
+        email_body = mock_send_mail_async.call_args[1]["email_body"]
+        self.assertTrue(f"La structure {self.siae.name } souhaite répondre en co-traitance" in email_body)
+
+        self.client.force_login(self.siae_user)
+        with mock.patch("lemarche.www.tenders.tasks.send_mail_async") as mock_send_mail_async:
+            response = self.client.post(url, data={})
+        self.assertContains(response, "Nous avons bien pris en compte votre demande de mise en relation")
+        mock_send_mail_async.assert_called_once()
+        email_body = mock_send_mail_async.call_args[1]["email_body"]
+        self.assertTrue(f"La structure {self.siae.name } souhaite répondre en co-traitance" in email_body)
+
+        user_without_siae = UserFactory(kind=User.KIND_SIAE)
+        self.client.force_login(user_without_siae)
+        with mock.patch("lemarche.www.tenders.tasks.send_mail_async") as mock_send_mail_async:
+            response = self.client.post(url, data={})
+        self.assertContains(response, "nous n'avons pas pu prendre en compte votre demande de mise en relation")
+        mock_send_mail_async.assert_not_called()
+
+
 # TODO: this test doesn't work anymore. find a way to test logging post-email in non-prod environments?
 # class TenderTasksTest(TestCase):
 #     @classmethod
diff --git a/lemarche/www/tenders/urls.py b/lemarche/www/tenders/urls.py
index 87b81324d..b28c8b12f 100644
--- a/lemarche/www/tenders/urls.py
+++ b/lemarche/www/tenders/urls.py
@@ -3,6 +3,7 @@
 
 from lemarche.www.tenders.views import (
     TenderCreateMultiStepView,
+    TenderDetailCocontractingClickView,
     TenderDetailContactClickStatView,
     TenderDetailSurveyTransactionedView,
     TenderDetailView,
@@ -32,6 +33,11 @@
     path(
         "<str:slug>/contact-click-stat", TenderDetailContactClickStatView.as_view(), name="detail-contact-click-stat"
     ),
+    path(
+        "<str:slug>/cocontracting-click",
+        TenderDetailCocontractingClickView.as_view(),
+        name="detail-cocontracting-click",
+    ),
     path(
         "<str:slug>/sondage-transaction",
         TenderDetailSurveyTransactionedView.as_view(),
diff --git a/lemarche/www/tenders/views.py b/lemarche/www/tenders/views.py
index 3738cd6e6..61f1879c0 100644
--- a/lemarche/www/tenders/views.py
+++ b/lemarche/www/tenders/views.py
@@ -32,6 +32,7 @@
     TenderCreateStepSurveyForm,
 )
 from lemarche.www.tenders.tasks import (  # , send_tender_emails_to_siaes
+    notify_admin_siae_wants_cocontracting,
     notify_admin_tender_created,
     send_siae_interested_email_to_author,
 )
@@ -403,6 +404,34 @@ def get_success_message(self, detail_contact_click_confirm):
         return f"<strong>{self.object.cta_card_button_text}</strong><br />Pour {self.object.cta_card_button_text.lower()}, vous devez accepter d'être mis en relation avec l'acheteur."  # noqa
 
 
+class TenderDetailCocontractingClickView(SiaeUserRequiredOrSiaeIdParamMixin, DetailView):
+    """
+    Endpoint to handle cocontracting button click
+    """
+
+    template_name = "tenders/_detail_cocontracting_click_confirm.html"
+    model = Tender
+
+    def get_object(self):
+        return get_object_or_404(Tender, slug=self.kwargs.get("slug"))
+
+    def post(self, request, *args, **kwargs):
+        self.object = self.get_object()
+        user = self.request.user
+
+        if self.request.user.is_authenticated:
+            siae = user.siaes.first()
+        else:
+            siae = Siae.objects.filter(pk=self.request.GET.get("siae_id", None)).first()
+
+        if siae:
+            notify_admin_siae_wants_cocontracting(self.object, siae)
+        else:
+            self.template_name = "tenders/_detail_cocontracting_click_error.html"
+
+        return self.get(request)
+
+
 class TenderSiaeListView(TenderAuthorOrAdminRequiredMixin, FormMixin, ListView):
     template_name = "tenders/siae_interested_list.html"
     form_class = SiaeFilterForm
