diff --git a/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/FirestoreClientImplTest.cs b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/FirestoreClientImplTest.cs
new file mode 100644
index 000000000000..cbf9f4b2c750
--- /dev/null
+++ b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/FirestoreClientImplTest.cs
@@ -0,0 +1,48 @@
+// Copyright 2019, Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System;
+using Xunit;
+
+namespace Google.Cloud.Firestore.V1.Tests
+{
+    public class FirestoreClientImplTest
+    {
+        [Theory]
+        [InlineData("projects/proj/databases/database", "projects/proj/databases/database")]
+        [InlineData("projects/proj/databases/database/", "projects/proj/databases/database")]
+        [InlineData("projects/proj/databases/database/documents", "projects/proj/databases/database")]
+        [InlineData("projects/proj/databases/database/documents/col1/doc", "projects/proj/databases/database")]
+        [InlineData("projects/proj_id/databases/(default)/foo", "projects/proj_id/databases/(default)")]
+        public void GetDatabaseResourceName_Valid(string resourceName, string expectedDatabaseName)
+        {
+            Assert.Equal(expectedDatabaseName, FirestoreClientImpl.GetDatabaseResourceName(resourceName));
+        }
+
+        [Theory]
+        [InlineData("")]
+        [InlineData("projects//databases/(default)/foo")]
+        [InlineData("not_projects/project/databases/(default)/foo")]
+        [InlineData("projects/proj/not_databases/database")]
+        [InlineData("projects/")]
+        [InlineData("projects/proj/")]
+        [InlineData("projects/proj/databases")]
+        [InlineData("projects/proj/databases/")]
+        [InlineData("projects/proj/databases//other")]
+        public void GetDatabaseResourceName_Invalid(string resourceName)
+        {
+            Assert.Throws<ArgumentException>(() => FirestoreClientImpl.GetDatabaseResourceName(resourceName));
+        }
+    }
+}
diff --git a/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/Google.Cloud.Firestore.V1.Tests.csproj b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/Google.Cloud.Firestore.V1.Tests.csproj
new file mode 100644
index 000000000000..f6516034c168
--- /dev/null
+++ b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/Google.Cloud.Firestore.V1.Tests.csproj
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFrameworks>net6.0;net462</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">net6.0</TargetFrameworks>
+    <IsPackable>false</IsPackable>
+    <NoWarn>1701;1702;1705;xUnit2004;xUnit2013</NoWarn>
+  </PropertyGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\tools\Google.Cloud.ClientTesting\Google.Cloud.ClientTesting.csproj" />
+    <ProjectReference Include="..\Google.Cloud.Firestore.V1\Google.Cloud.Firestore.V1.csproj" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(TestSdkVersion)" />
+    <PackageReference Include="NSubstitute" Version="$(NSubstituteVersion)" />
+    <PackageReference Include="System.Linq.Async" Version="$(SystemLinqAsyncVersion)" />
+    <PackageReference Include="Xunit.SkippableFact" Version="$(XUnitSkippableFactVersion)" />
+    <PackageReference Include="xunit" Version="$(XUnitVersion)" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="$(XUnitRunnerVersion)" />
+    <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/coverage.xml b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/coverage.xml
new file mode 100644
index 000000000000..a8ebb3857262
--- /dev/null
+++ b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.Tests/coverage.xml
@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="utf-8"?>
+<CoverageParams>
+  <TargetExecutable>C:/Program Files/dotnet/dotnet.exe</TargetExecutable>
+  <TargetArguments>test --no-build -c Release</TargetArguments>
+  <Filters>
+    <IncludeFilters>
+      <FilterEntry>
+        <ModuleMask>Google.Cloud.Firestore.V1</ModuleMask>
+      </FilterEntry>
+    </IncludeFilters>
+  </Filters>
+  <AttributeFilters>
+    <AttributeFilterEntry>System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverageAttribute</AttributeFilterEntry>
+    <AttributeFilterEntry>System.Diagnostics.DebuggerNonUserCodeAttribute</AttributeFilterEntry>
+  </AttributeFilters>
+  <TargetWorkingDir>.</TargetWorkingDir>
+  <Output>../../../coverage/Google.Cloud.Firestore.V1.Tests.dvcr</Output>
+</CoverageParams>
\ No newline at end of file
diff --git a/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.sln b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.sln
index 336cb37bab57..89fbcf78e138 100644
--- a/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.sln
+++ b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1.sln
@@ -3,19 +3,24 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.0.31903.59
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Google.Cloud.Firestore.V1", "Google.Cloud.Firestore.V1\Google.Cloud.Firestore.V1.csproj", "{F9CE8ABD-FB0E-437E-B03A-27F52D7A9F9A}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Google.Cloud.Firestore.V1", "Google.Cloud.Firestore.V1\Google.Cloud.Firestore.V1.csproj", "{F9CE8ABD-FB0E-437E-B03A-27F52D7A9F9A}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Google.Cloud.Firestore.V1.GeneratedSnippets", "Google.Cloud.Firestore.V1.GeneratedSnippets\Google.Cloud.Firestore.V1.GeneratedSnippets.csproj", "{F841636E-5304-4C09-B151-7B1DDB0618C8}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Google.Cloud.Firestore.V1.GeneratedSnippets", "Google.Cloud.Firestore.V1.GeneratedSnippets\Google.Cloud.Firestore.V1.GeneratedSnippets.csproj", "{F841636E-5304-4C09-B151-7B1DDB0618C8}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Google.Cloud.ClientTesting", "..\..\tools\Google.Cloud.ClientTesting\Google.Cloud.ClientTesting.csproj", "{99487E3D-9DFC-419B-95AC-F8D5BEE8A3A4}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Google.Cloud.ClientTesting", "..\..\tools\Google.Cloud.ClientTesting\Google.Cloud.ClientTesting.csproj", "{99487E3D-9DFC-419B-95AC-F8D5BEE8A3A4}"
 EndProject
-Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Google.Cloud.Firestore.V1.Snippets", "Google.Cloud.Firestore.V1.Snippets\Google.Cloud.Firestore.V1.Snippets.csproj", "{4357F6C5-8599-41D7-84EF-ED59E32B54DF}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Google.Cloud.Firestore.V1.Snippets", "Google.Cloud.Firestore.V1.Snippets\Google.Cloud.Firestore.V1.Snippets.csproj", "{4357F6C5-8599-41D7-84EF-ED59E32B54DF}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Google.Cloud.Firestore.V1.Tests", "Google.Cloud.Firestore.V1.Tests\Google.Cloud.Firestore.V1.Tests.csproj", "{8C638D13-3585-4344-B597-DA0EA0266688}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
 		Release|Any CPU = Release|Any CPU
 	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
 	GlobalSection(ProjectConfigurationPlatforms) = postSolution
 		{F9CE8ABD-FB0E-437E-B03A-27F52D7A9F9A}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{F9CE8ABD-FB0E-437E-B03A-27F52D7A9F9A}.Debug|Any CPU.Build.0 = Debug|Any CPU
@@ -33,11 +38,9 @@ Global
 		{4357F6C5-8599-41D7-84EF-ED59E32B54DF}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{4357F6C5-8599-41D7-84EF-ED59E32B54DF}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{4357F6C5-8599-41D7-84EF-ED59E32B54DF}.Release|Any CPU.Build.0 = Release|Any CPU
-	EndGlobalSection
-	GlobalSection(SolutionProperties) = preSolution
-		HideSolutionNode = FALSE
-	EndGlobalSection
-	GlobalSection(ExtensibilityGlobals) = postSolution
-		SolutionGuid = {A454C46B-D941-47B5-A3BD-218EC33797BE}
+		{8C638D13-3585-4344-B597-DA0EA0266688}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{8C638D13-3585-4344-B597-DA0EA0266688}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{8C638D13-3585-4344-B597-DA0EA0266688}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{8C638D13-3585-4344-B597-DA0EA0266688}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal
diff --git a/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1/FirestoreClientPartial.cs b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1/FirestoreClientPartial.cs
index 58bd803464bf..35d7ca38cdc0 100644
--- a/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1/FirestoreClientPartial.cs
+++ b/apis/Google.Cloud.Firestore.V1/Google.Cloud.Firestore.V1/FirestoreClientPartial.cs
@@ -54,6 +54,100 @@ public partial class FirestoreClientImpl
         [Obsolete("This header is obsolete; x-goog-request-params should now be used instead. " +
             "This constant will be removed in a future version")]
         public const string ResourcePrefixHeader = "google-cloud-resource-prefix";
+
+        partial void Modify_BatchGetDocumentsRequest(ref BatchGetDocumentsRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Database);
+
+        partial void Modify_BeginTransactionRequest(ref BeginTransactionRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Database);
+
+        partial void Modify_CommitRequest(ref CommitRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Database);
+
+        partial void Modify_CreateDocumentRequest(ref CreateDocumentRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Parent);
+
+        partial void Modify_DeleteDocumentRequest(ref DeleteDocumentRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Name);
+
+        partial void Modify_GetDocumentRequest(ref GetDocumentRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Name);
+
+        partial void Modify_ListCollectionIdsRequest(ref ListCollectionIdsRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Parent);
+
+        partial void Modify_ListDocumentsRequest(ref ListDocumentsRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Parent);
+
+        partial void Modify_RollbackRequest(ref RollbackRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Database);
+
+        partial void Modify_RunQueryRequest(ref RunQueryRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Parent);
+
+        partial void Modify_RunAggregationQueryRequest(ref RunAggregationQueryRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Parent);
+
+        partial void Modify_UpdateDocumentRequest(ref UpdateDocumentRequest request, ref CallSettings settings) =>
+            ApplyResourcePrefixHeader(ref settings, request.Document?.Name);
+
+        private static void ApplyResourcePrefixHeader(ref CallSettings settings, string resource)
+        {
+            // If we haven't been given a resource name, just let the request as it is.
+            if (string.IsNullOrEmpty(resource))
+            {
+                return;
+            }
+            string database = GetDatabaseResourceName(resource);
+#pragma warning disable CS0618 // Type or member is obsolete
+            settings = settings.WithHeader(ResourcePrefixHeader, database);
+#pragma warning restore CS0618 // Type or member is obsolete
+        }
+
+        // Visible for testing
+
+        /// <summary>
+        /// Retrieves the database resource name from a full resource name.
+        /// Validation is performed as far as the database ID but no further; the database ID is deemed to end at the first slash.
+        /// </summary>
+        /// <param name="resource">The resource name, which must start with projects/{project_id}/databases/{database_id}</param>
+        /// <returns>The database resource name</returns>
+        internal static string GetDatabaseResourceName(string resource)
+        {
+            const string projectsPrefix = "projects/";
+            const string databasesPrefix = "databases/";
+            if (string.CompareOrdinal(resource, 0, projectsPrefix, 0, projectsPrefix.Length) != 0)
+            {
+                // "projects/" doesn't match
+                ThrowInvalidResource();
+            }
+            int endOfProjectId = resource.IndexOf('/', projectsPrefix.Length);
+            if (endOfProjectId == -1 || endOfProjectId == projectsPrefix.Length)
+            {
+                // Empty project ID or no slash at the end of it
+                ThrowInvalidResource();
+            }
+            if (string.CompareOrdinal(resource, endOfProjectId + 1, databasesPrefix, 0, databasesPrefix.Length) != 0)
+            {
+                // "databases/" doesn't match
+                ThrowInvalidResource();
+            }
+            int startOfDatabaseId = endOfProjectId + 1 + databasesPrefix.Length;
+            if (startOfDatabaseId == resource.Length)
+            {
+                // No database ID
+                ThrowInvalidResource();
+            }
+            int endOfDatabaseId = resource.IndexOf('/', startOfDatabaseId);
+            if (endOfDatabaseId == startOfDatabaseId)
+            {
+                ThrowInvalidResource();
+            }
+            // It's valid for the whole resource name to be the database name
+            return endOfDatabaseId == -1 ? resource : resource.Substring(0, endOfDatabaseId);
+
+            void ThrowInvalidResource() => throw new ArgumentException($"{resource} is not a valid Firestore resource name", nameof(resource));
+        }
     }
 
     // Support for FirestoreDbBuilder.