diff --git a/services/acl/Acl.Application/AclService.cs b/services/acl/Acl.Application/AclService.cs
index 4b23964..34c0ced 100644
--- a/services/acl/Acl.Application/AclService.cs
+++ b/services/acl/Acl.Application/AclService.cs
@@ -42,6 +42,12 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, IZaak
         await gateway.SetZaakToCancellationStatusAsync(zaakUrl, await catalog.GetZaaktypeUrlAsync(ct), clock.Today, ct);
     }
 
+    /// <summary>The published zaaktypen, for the beheer catalogus viewer (S-15a). Read-only passthrough:
+    /// no default-fill, the ACL is simply the only code allowed to read ZGW (§8.1).</summary>
+    public Task<IReadOnlyList<ZaaktypeSummary>> ListZaaktypenAsync(CancellationToken ct = default) =>
+        // ponytail: stub for the red test; real passthrough lands in the green commit.
+        Task.FromResult<IReadOnlyList<ZaaktypeSummary>>([]);
+
     /// <summary>The zaak's reference (its ZGW identificatie), for the read projection (#78).</summary>
     public Task<string> GetZaakReferenceAsync(Uri zaakUrl, CancellationToken ct = default)
     {
diff --git a/services/acl/Acl.Application/IZaakGateway.cs b/services/acl/Acl.Application/IZaakGateway.cs
index 3848d8b..d3620ec 100644
--- a/services/acl/Acl.Application/IZaakGateway.cs
+++ b/services/acl/Acl.Application/IZaakGateway.cs
@@ -40,4 +40,8 @@ public interface IZaakGateway
     /// <summary>Resolve the URL of the published informatieobjecttype with the given
     /// <paramref name="omschrijving"/> from the Catalogi API (S-27). Throws if none matches.</summary>
     Task<Uri> ResolveInformatieobjecttypeUrlAsync(string omschrijving, CancellationToken ct = default);
+
+    /// <summary>List the published zaaktypen from the Catalogi API — the read-only catalogus the beheer
+    /// portal shows (S-15a). The ACL is the only code allowed to read ZGW (§8.1).</summary>
+    Task<IReadOnlyList<ZaaktypeSummary>> ListZaaktypenAsync(CancellationToken ct = default);
 }
diff --git a/services/acl/Acl.Application/ZaaktypeSummary.cs b/services/acl/Acl.Application/ZaaktypeSummary.cs
new file mode 100644
index 0000000..8c93d05
--- /dev/null
+++ b/services/acl/Acl.Application/ZaaktypeSummary.cs
@@ -0,0 +1,6 @@
+namespace Acl.Application;
+
+/// <summary>A published zaaktype as the beheer catalogus viewer shows it (S-15a). Public-safe: the
+/// business <see cref="Identificatie"/> + human <see cref="Omschrijving"/> and the ZGW <see cref="Url"/>
+/// (the URL is the ACL's own reference, not shown to end users).</summary>
+public sealed record ZaaktypeSummary(string Identificatie, string Omschrijving, Uri Url);
diff --git a/services/acl/Acl.Infrastructure/OpenZaakGateway.cs b/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
index 156b810..1978a4f 100644
--- a/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
+++ b/services/acl/Acl.Infrastructure/OpenZaakGateway.cs
@@ -170,6 +170,10 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         return new Uri(match.Url);
     }
 
+    public Task<IReadOnlyList<ZaaktypeSummary>> ListZaaktypenAsync(CancellationToken ct = default) =>
+        // ponytail: stub for the red test; real Catalogi read lands in the green commit.
+        throw new NotImplementedException();
+
     // GETs an absolute-by-path ZGW resource with auth (no CRS — catalogi is not a geo API).
     private async Task<T> GetAsync<T>(string pathAndQuery, string label, CancellationToken ct)
     {
diff --git a/services/acl/Acl.Tests/AclServiceTests.cs b/services/acl/Acl.Tests/AclServiceTests.cs
index 930d380..905dc9f 100644
--- a/services/acl/Acl.Tests/AclServiceTests.cs
+++ b/services/acl/Acl.Tests/AclServiceTests.cs
@@ -65,6 +65,14 @@ public class AclServiceTests
             ResolvedByOmschrijving = omschrijving;
             return Task.FromResult(ResolvedInformatieobjecttype);
         }
+
+        public IReadOnlyList<ZaaktypeSummary> Zaaktypen { get; } =
+        [
+            new("BIG-REGISTRATIE", "BIG-registratie", new Uri("http://openzaak/catalogi/api/v1/zaaktypen/big")),
+        ];
+
+        public Task<IReadOnlyList<ZaaktypeSummary>> ListZaaktypenAsync(CancellationToken ct = default) =>
+            Task.FromResult(Zaaktypen);
     }
 
     private static AclDefaults Defaults() => new()
@@ -225,4 +233,18 @@ public class AclServiceTests
         await Assert.ThrowsAsync<ArgumentNullException>(() => service.GetZaakReferenceAsync(null!));
         Assert.Null(gateway.ReadReferenceFor);
     }
+
+    [Fact]
+    public async Task Listing_zaaktypen_returns_the_gateways_published_zaaktypen(/* S-15a */)
+    {
+        var gateway = new FakeGateway();
+        var service = ServiceWith(gateway, Defaults(), new DateOnly(2026, 6, 4));
+
+        var zaaktypen = await service.ListZaaktypenAsync();
+
+        var only = Assert.Single(zaaktypen);
+        Assert.Equal("BIG-REGISTRATIE", only.Identificatie);
+        Assert.Equal("BIG-registratie", only.Omschrijving);
+        Assert.Equal(new Uri("http://openzaak/catalogi/api/v1/zaaktypen/big"), only.Url);
+    }
 }
diff --git a/services/acl/Acl.Tests/ZaaktypeCatalogTests.cs b/services/acl/Acl.Tests/ZaaktypeCatalogTests.cs
index 8f3f7f6..117b00c 100644
--- a/services/acl/Acl.Tests/ZaaktypeCatalogTests.cs
+++ b/services/acl/Acl.Tests/ZaaktypeCatalogTests.cs
@@ -36,6 +36,7 @@ public class ZaaktypeCatalogTests
         public Task SetZaakToCancellationStatusAsync(Uri z, Uri zt, DateOnly d, CancellationToken ct = default) => throw new NotSupportedException();
         public Task<string> GetZaakIdentificatieAsync(Uri z, CancellationToken ct = default) => throw new NotSupportedException();
         public Task<Uri> StoreDocumentAsync(DocumentRequest r, CancellationToken ct = default) => throw new NotSupportedException();
+        public Task<IReadOnlyList<ZaaktypeSummary>> ListZaaktypenAsync(CancellationToken ct = default) => throw new NotSupportedException();
     }
 
     private static AclDefaults Defaults() => new()