diff --git a/src/ZB.MOM.WW.OtOpcUa.Core/OpcUa/IdentificationFolderBuilder.cs b/src/ZB.MOM.WW.OtOpcUa.Core/OpcUa/IdentificationFolderBuilder.cs
new file mode 100644
index 0000000..cb28e36
--- /dev/null
+++ b/src/ZB.MOM.WW.OtOpcUa.Core/OpcUa/IdentificationFolderBuilder.cs
@@ -0,0 +1,91 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+/// <summary>
+///     Phase 6.4 Stream D: materializes the OPC 40010 Machinery companion-spec Identification
+///     sub-folder under an Equipment node. Reads the nine decision-#139 columns off the
+///     <see cref="Equipment"/> row and emits one property per non-null field.
+/// </summary>
+/// <remarks>
+///     <para>Pure-function shape — testable without a real OPC UA node manager. The caller
+///     passes the builder scoped to the Equipment node; this class handles the Identification
+///     sub-folder creation + per-field <see cref="IAddressSpaceBuilder.AddProperty"/> calls.</para>
+///
+///     <para>ACL binding: the sub-folder + its properties inherit the Equipment scope's
+///     grants (no new scope level). Phase 6.2's trie treats them as part of the Equipment
+///     ScopeId — a user with Equipment-level grant reads Identification; a user without the
+///     grant gets BadUserAccessDenied on both the Equipment node + its Identification variables.
+///     See <c>docs/v2/acl-design.md</c> §Identification cross-reference.</para>
+///
+///     <para>The nine fields per decision #139 are exposed exactly when they carry a non-null
+///     value. A row with all nine null produces no Identification sub-folder at all — the
+///     caller can use <see cref="HasAnyFields(Equipment)"/> to skip the Folder call entirely
+///     and avoid a pointless empty folder appearing in browse trees.</para>
+/// </remarks>
+public static class IdentificationFolderBuilder
+{
+    /// <summary>Browse + display name of the sub-folder — fixed per OPC 40010 convention.</summary>
+    public const string FolderName = "Identification";
+
+    /// <summary>
+    ///     Canonical decision #139 field set exposed in the Identification sub-folder. Order
+    ///     matches the decision-log entry so any browse-order reader can cross-reference
+    ///     without re-sorting.
+    /// </summary>
+    public static IReadOnlyList<string> FieldNames { get; } = new[]
+    {
+        "Manufacturer", "Model", "SerialNumber",
+        "HardwareRevision", "SoftwareRevision",
+        "YearOfConstruction", "AssetLocation",
+        "ManufacturerUri", "DeviceManualUri",
+    };
+
+    /// <summary>True when the equipment row has at least one non-null Identification field.</summary>
+    public static bool HasAnyFields(Equipment equipment)
+    {
+        ArgumentNullException.ThrowIfNull(equipment);
+        return equipment.Manufacturer is not null
+            || equipment.Model is not null
+            || equipment.SerialNumber is not null
+            || equipment.HardwareRevision is not null
+            || equipment.SoftwareRevision is not null
+            || equipment.YearOfConstruction is not null
+            || equipment.AssetLocation is not null
+            || equipment.ManufacturerUri is not null
+            || equipment.DeviceManualUri is not null;
+    }
+
+    /// <summary>
+    ///     Build the Identification sub-folder under <paramref name="equipmentBuilder"/>. No-op
+    ///     when every field is null. Returns the sub-folder builder (or null when no-op) so
+    ///     callers can attach additional nodes underneath if needed.
+    /// </summary>
+    public static IAddressSpaceBuilder? Build(IAddressSpaceBuilder equipmentBuilder, Equipment equipment)
+    {
+        ArgumentNullException.ThrowIfNull(equipmentBuilder);
+        ArgumentNullException.ThrowIfNull(equipment);
+
+        if (!HasAnyFields(equipment)) return null;
+
+        var folder = equipmentBuilder.Folder(FolderName, FolderName);
+        AddIfPresent(folder, "Manufacturer",       DriverDataType.String,   equipment.Manufacturer);
+        AddIfPresent(folder, "Model",              DriverDataType.String,   equipment.Model);
+        AddIfPresent(folder, "SerialNumber",       DriverDataType.String,   equipment.SerialNumber);
+        AddIfPresent(folder, "HardwareRevision",   DriverDataType.String,   equipment.HardwareRevision);
+        AddIfPresent(folder, "SoftwareRevision",   DriverDataType.String,   equipment.SoftwareRevision);
+        AddIfPresent(folder, "YearOfConstruction", DriverDataType.Int32,
+            equipment.YearOfConstruction is null ? null : (object)(int)equipment.YearOfConstruction.Value);
+        AddIfPresent(folder, "AssetLocation",      DriverDataType.String,   equipment.AssetLocation);
+        AddIfPresent(folder, "ManufacturerUri",    DriverDataType.String,   equipment.ManufacturerUri);
+        AddIfPresent(folder, "DeviceManualUri",    DriverDataType.String,   equipment.DeviceManualUri);
+        return folder;
+    }
+
+    private static void AddIfPresent(IAddressSpaceBuilder folder, string name, DriverDataType dataType, object? value)
+    {
+        if (value is null) return;
+        folder.AddProperty(name, dataType, value);
+    }
+}
diff --git a/tests/ZB.MOM.WW.OtOpcUa.Core.Tests/OpcUa/IdentificationFolderBuilderTests.cs b/tests/ZB.MOM.WW.OtOpcUa.Core.Tests/OpcUa/IdentificationFolderBuilderTests.cs
new file mode 100644
index 0000000..d1ba349
--- /dev/null
+++ b/tests/ZB.MOM.WW.OtOpcUa.Core.Tests/OpcUa/IdentificationFolderBuilderTests.cs
@@ -0,0 +1,158 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.OpcUa;
+
+[Trait("Category", "Unit")]
+public sealed class IdentificationFolderBuilderTests
+{
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = [];
+        public List<(string BrowseName, DriverDataType DataType, object? Value)> Properties { get; } = [];
+
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+        {
+            Folders.Add((browseName, displayName));
+            return this; // flat recording — identification fields land in the same bucket
+        }
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo attributeInfo)
+            => throw new NotSupportedException("Identification fields use AddProperty, not Variable");
+
+        public void AddProperty(string browseName, DriverDataType dataType, object? value)
+            => Properties.Add((browseName, dataType, value));
+    }
+
+    private static Equipment EmptyEquipment() => new()
+    {
+        EquipmentId = "EQ-000000000001",
+        DriverInstanceId = "drv-1",
+        UnsLineId = "line-1",
+        Name = "eq-1",
+        MachineCode = "machine_001",
+    };
+
+    private static Equipment FullyPopulatedEquipment() => new()
+    {
+        EquipmentId = "EQ-000000000001",
+        DriverInstanceId = "drv-1",
+        UnsLineId = "line-1",
+        Name = "eq-1",
+        MachineCode = "machine_001",
+        Manufacturer = "Siemens",
+        Model = "S7-1500",
+        SerialNumber = "SN-12345",
+        HardwareRevision = "Rev-A",
+        SoftwareRevision = "Fw-2.3.1",
+        YearOfConstruction = 2023,
+        AssetLocation = "Warsaw-West/Bldg-3",
+        ManufacturerUri = "https://siemens.example",
+        DeviceManualUri = "https://siemens.example/manual",
+    };
+
+    [Fact]
+    public void HasAnyFields_AllNull_ReturnsFalse()
+    {
+        IdentificationFolderBuilder.HasAnyFields(EmptyEquipment()).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void HasAnyFields_OneNonNull_ReturnsTrue()
+    {
+        var eq = EmptyEquipment();
+        eq.SerialNumber = "SN-1";
+        IdentificationFolderBuilder.HasAnyFields(eq).ShouldBeTrue();
+    }
+
+    [Fact]
+    public void Build_AllNull_ReturnsNull_AndDoesNotEmit_Folder()
+    {
+        var builder = new RecordingBuilder();
+
+        var result = IdentificationFolderBuilder.Build(builder, EmptyEquipment());
+
+        result.ShouldBeNull();
+        builder.Folders.ShouldBeEmpty("no Identification folder when every field is null");
+        builder.Properties.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Build_FullyPopulated_EmitsAllNineFields()
+    {
+        var builder = new RecordingBuilder();
+
+        var result = IdentificationFolderBuilder.Build(builder, FullyPopulatedEquipment());
+
+        result.ShouldNotBeNull();
+        builder.Folders.ShouldContain(f => f.BrowseName == "Identification");
+        builder.Properties.Count.ShouldBe(9);
+        builder.Properties.Select(p => p.BrowseName).ShouldBe(
+            ["Manufacturer", "Model", "SerialNumber",
+             "HardwareRevision", "SoftwareRevision",
+             "YearOfConstruction", "AssetLocation",
+             "ManufacturerUri", "DeviceManualUri"],
+            "property order matches decision #139 exactly");
+    }
+
+    [Fact]
+    public void Build_OnlyNonNull_Are_Emitted()
+    {
+        var eq = EmptyEquipment();
+        eq.Manufacturer = "Siemens";
+        eq.SerialNumber = "SN-1";
+        eq.YearOfConstruction = 2024;
+        var builder = new RecordingBuilder();
+
+        IdentificationFolderBuilder.Build(builder, eq);
+
+        builder.Properties.Count.ShouldBe(3, "only the 3 non-null fields are exposed");
+        builder.Properties.Select(p => p.BrowseName).ShouldBe(
+            ["Manufacturer", "SerialNumber", "YearOfConstruction"]);
+    }
+
+    [Fact]
+    public void YearOfConstruction_Maps_Short_To_Int32_DriverDataType()
+    {
+        var eq = EmptyEquipment();
+        eq.YearOfConstruction = 2023;
+        var builder = new RecordingBuilder();
+
+        IdentificationFolderBuilder.Build(builder, eq);
+
+        var prop = builder.Properties.Single(p => p.BrowseName == "YearOfConstruction");
+        prop.DataType.ShouldBe(DriverDataType.Int32);
+        prop.Value.ShouldBe(2023, "short is widened to int for OPC UA Int32 representation");
+    }
+
+    [Fact]
+    public void Build_StringValues_RoundTrip()
+    {
+        var eq = FullyPopulatedEquipment();
+        var builder = new RecordingBuilder();
+
+        IdentificationFolderBuilder.Build(builder, eq);
+
+        builder.Properties.Single(p => p.BrowseName == "Manufacturer").Value.ShouldBe("Siemens");
+        builder.Properties.Single(p => p.BrowseName == "DeviceManualUri").Value.ShouldBe("https://siemens.example/manual");
+    }
+
+    [Fact]
+    public void FieldNames_Match_Decision139_Exactly()
+    {
+        IdentificationFolderBuilder.FieldNames.ShouldBe(
+            ["Manufacturer", "Model", "SerialNumber",
+             "HardwareRevision", "SoftwareRevision",
+             "YearOfConstruction", "AssetLocation",
+             "ManufacturerUri", "DeviceManualUri"]);
+    }
+
+    [Fact]
+    public void FolderName_Is_Identification()
+    {
+        IdentificationFolderBuilder.FolderName.ShouldBe("Identification");
+    }
+}