diff --git a/Makefile b/Makefile
index 60a648e..49442f5 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@
 # `make ci` locally runs exactly what the pipeline runs — no drift. Until a
 # self-hosted runner is registered, `make ci` is the gate (see docs/runbooks/ci.md).
 
-SLN        := services/bff/Bff.slnx
+SLN        := register-referentie.slnx
 COMPOSE    := infra/docker-compose.yml
 HEALTH_URL := http://localhost:8080/health
 OZ_COMPOSE  := infra/openzaak/docker-compose.yml
diff --git a/register-referentie.slnx b/register-referentie.slnx
new file mode 100644
index 0000000..bf80fac
--- /dev/null
+++ b/register-referentie.slnx
@@ -0,0 +1,13 @@
+<Solution>
+  <Folder Name="/services/" />
+  <Folder Name="/services/acl/">
+    <Project Path="services/acl/Acl.Api/Acl.Api.csproj" />
+    <Project Path="services/acl/Acl.Application/Acl.Application.csproj" />
+    <Project Path="services/acl/Acl.Infrastructure/Acl.Infrastructure.csproj" />
+    <Project Path="services/acl/Acl.Tests/Acl.Tests.csproj" />
+  </Folder>
+  <Folder Name="/services/bff/">
+    <Project Path="services/bff/Bff.Api/Bff.Api.csproj" />
+    <Project Path="services/bff/Bff.Tests/Bff.Tests.csproj" />
+  </Folder>
+</Solution>
diff --git a/services/acl/Acl.Application/AclService.cs b/services/acl/Acl.Application/AclService.cs
index effb09d..e285ee7 100644
--- a/services/acl/Acl.Application/AclService.cs
+++ b/services/acl/Acl.Application/AclService.cs
@@ -5,5 +5,16 @@ namespace Acl.Application;
 public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, IClock clock)
 {
     public Task<Uri> OpenZaakAsync(DomainRegistration registration, CancellationToken ct = default)
-        => throw new NotImplementedException();
+    {
+        ArgumentNullException.ThrowIfNull(registration);
+
+        var request = new ZaakRequest(
+            defaults.Bronorganisatie,
+            defaults.VerantwoordelijkeOrganisatie,
+            defaults.Vertrouwelijkheidaanduiding,
+            defaults.ZaaktypeUrl,
+            clock.Today);
+
+        return gateway.OpenZaakAsync(request, ct);
+    }
 }
diff --git a/services/acl/Acl.Infrastructure/OpenZaakGateway.cs b/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
index 3332a1e..0a6e2e4 100644
--- a/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
+++ b/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
@@ -1,3 +1,6 @@
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using System.Text.Json.Serialization;
 using Acl.Application;
 
 namespace Acl.Infrastructure;
@@ -5,6 +8,41 @@ namespace Acl.Infrastructure;
 /// <summary>The only code that talks to OpenZaak's Zaken API (ADR-0001).</summary>
 public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) : IZaakGateway
 {
-    public Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default)
-        => throw new NotImplementedException();
+    public async Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(request);
+
+        using var message = new HttpRequestMessage(
+            HttpMethod.Post, new Uri(options.BaseUrl, "/zaken/api/v1/zaken"))
+        {
+            Content = JsonContent.Create(new ZaakDto(
+                request.Bronorganisatie,
+                request.Zaaktype.ToString(),
+                request.VerantwoordelijkeOrganisatie,
+                request.Startdatum.ToString("yyyy-MM-dd"),
+                request.Vertrouwelijkheidaanduiding)),
+        };
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+        // ZRC is a geo API; it requires the CRS headers.
+        message.Headers.Add("Accept-Crs", "EPSG:4326");
+        message.Content.Headers.Add("Content-Crs", "EPSG:4326");
+
+        using var response = await http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+
+        var created = await response.Content.ReadFromJsonAsync<ZaakCreatedDto>(ct)
+            ?? throw new InvalidOperationException("OpenZaak returned an empty zaak response");
+        return new Uri(created.Url);
+    }
+
+    private sealed record ZaakDto(
+        [property: JsonPropertyName("bronorganisatie")] string Bronorganisatie,
+        [property: JsonPropertyName("zaaktype")] string Zaaktype,
+        [property: JsonPropertyName("verantwoordelijkeOrganisatie")] string VerantwoordelijkeOrganisatie,
+        [property: JsonPropertyName("startdatum")] string Startdatum,
+        [property: JsonPropertyName("vertrouwelijkheidaanduiding")] string Vertrouwelijkheidaanduiding);
+
+    private sealed record ZaakCreatedDto(
+        [property: JsonPropertyName("url")] string Url);
 }