diff --git a/.props/Test.props b/.props/Test.props
index 38bffa770b..6d971f7b8f 100644
--- a/.props/Test.props
+++ b/.props/Test.props
@@ -35,4 +35,8 @@
     <RunAnalyzers>false</RunAnalyzers>
   </PropertyGroup>
 
+  <PropertyGroup>
+        <NoWarn>$(NoWarn),CS0618</NoWarn> <!-- Instrumentation Key based APIs have been marked Obsolete. No plans to update the tests at this time. -->
+  </PropertyGroup>
+
 </Project>
diff --git a/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/TelemetryConfigurationFactory.cs b/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/TelemetryConfigurationFactory.cs
index 004f10af65..d00d73a551 100644
--- a/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/TelemetryConfigurationFactory.cs
+++ b/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/TelemetryConfigurationFactory.cs
@@ -477,7 +477,9 @@ private static void SelectInstrumentationKey(TelemetryConfiguration configuratio
             else if (PlatformSingleton.Current.TryGetEnvironmentVariable(InstrumentationKeyEnvironmentVariable, out string instrumentationKeyEnVar))
             {
                 CoreEventSource.Log.TelemetryConfigurationFactoryFoundInstrumentationKeyEnvironmentVariable(variableName: InstrumentationKeyEnvironmentVariable);
+#pragma warning disable CS0618 // Type or member is obsolete
                 configuration.InstrumentationKey = instrumentationKeyEnVar;
+#pragma warning restore CS0618 // Type or member is obsolete
             }
 
             // SANITY CHECK - If Ikey is null, this means that neither the InstrumentationKey nor ConnectionString were set.
diff --git a/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/Tracing/HeartbeatProvider.cs b/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/Tracing/HeartbeatProvider.cs
index 2dfef202d3..c9cead3c61 100644
--- a/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/Tracing/HeartbeatProvider.cs
+++ b/BASE/src/Microsoft.ApplicationInsights/Extensibility/Implementation/Tracing/HeartbeatProvider.cs
@@ -103,7 +103,9 @@ public string InstrumentationKey
             {
                 if (this.telemetryClient != null)
                 {
+#pragma warning disable CS0618 // Type or member is obsolete
                     this.telemetryClient.InstrumentationKey = value;
+#pragma warning restore CS0618 // Type or member is obsolete
                 }
             }
         }
diff --git a/BASE/src/Microsoft.ApplicationInsights/Extensibility/TelemetryConfiguration.cs b/BASE/src/Microsoft.ApplicationInsights/Extensibility/TelemetryConfiguration.cs
index 53d284b666..1de1e0a5b6 100644
--- a/BASE/src/Microsoft.ApplicationInsights/Extensibility/TelemetryConfiguration.cs
+++ b/BASE/src/Microsoft.ApplicationInsights/Extensibility/TelemetryConfiguration.cs
@@ -74,7 +74,9 @@ static TelemetryConfiguration()
         /// Initializes a new instance of the TelemetryConfiguration class.
         /// </summary>
         [EditorBrowsable(EditorBrowsableState.Never)]
+#pragma warning disable CS0618 // Type or member is obsolete
         public TelemetryConfiguration() : this(string.Empty, null)
+#pragma warning restore CS0618 // Type or member is obsolete
         {
         }
 
@@ -82,6 +84,7 @@ public TelemetryConfiguration() : this(string.Empty, null)
         /// Initializes a new instance of the TelemetryConfiguration class.
         /// </summary>
         /// <param name="instrumentationKey">The instrumentation key this configuration instance will provide.</param>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use the default constructor and manually set TelemetryConfiguration.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         public TelemetryConfiguration(string instrumentationKey) : this(instrumentationKey, null)
         {
         }
@@ -91,6 +94,7 @@ public TelemetryConfiguration(string instrumentationKey) : this(instrumentationK
         /// </summary>
         /// <param name="instrumentationKey">The instrumentation key this configuration instance will provide.</param>
         /// <param name="channel">The telemetry channel to provide with this configuration instance.</param>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use the default constructor and manually set TelemetryConfiguration.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         public TelemetryConfiguration(string instrumentationKey, ITelemetryChannel channel)
         {
             this.instrumentationKey = instrumentationKey ?? throw new ArgumentNullException(nameof(instrumentationKey));
@@ -149,8 +153,9 @@ internal set
         /// </remarks>
         public string InstrumentationKey
         {
-            get { return this.instrumentationKey; }
+            get => this.instrumentationKey;
 
+            [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use TelemetryConfiguration.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
             set { this.instrumentationKey = value ?? throw new ArgumentNullException(nameof(this.InstrumentationKey)); }
         }
 
@@ -296,7 +301,9 @@ public string ConnectionString
                         ConnectionString = value,
                     };
 
+#pragma warning disable CS0618 // Type or member is obsolete
                     this.InstrumentationKey = endpointProvider.GetInstrumentationKey();
+#pragma warning restore CS0618 // Type or member is obsolete
 
                     this.EndpointContainer = new EndpointContainer(endpointProvider);
 
diff --git a/BASE/src/Microsoft.ApplicationInsights/TelemetryClient.cs b/BASE/src/Microsoft.ApplicationInsights/TelemetryClient.cs
index 9218e60256..8cf1cf6720 100644
--- a/BASE/src/Microsoft.ApplicationInsights/TelemetryClient.cs
+++ b/BASE/src/Microsoft.ApplicationInsights/TelemetryClient.cs
@@ -79,7 +79,9 @@ public TelemetryContext Context
         /// </summary>
         public string InstrumentationKey
         {
-            get { return this.Context.InstrumentationKey; }
+            get => this.Context.InstrumentationKey;
+
+            [Obsolete("InstrumentationKey based global ingestion is being deprecated. Recommended to set TelemetryConfiguration.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
             set { this.Context.InstrumentationKey = value; }
         }
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a34b915e20..e8dcc57261 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,8 @@
 - [Added support for distributed tracing with Azure.Messaging.ServiceBus](https://github.com/microsoft/ApplicationInsights-dotnet/pull/2593)
 - [Move internal type from `Shared` to `Microsoft` namespace](https://github.com/microsoft/ApplicationInsights-dotnet/pull/2442)
 - [Extension methods to retrive specific operation details.](https://github.com/microsoft/ApplicationInsights-dotnet/issues/1350)
+- [Mark Instrumentation Key based APIs as Obsolete](https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560).
+  - See also: https://docs.microsoft.com/azure/azure-monitor/app/migrate-from-instrumentation-keys-to-connection-strings
 
 ## Version 2.21.0-beta1
 - [Support IPv6 in request headers](https://github.com/microsoft/ApplicationInsights-dotnet/issues/2521)
diff --git a/LOGGING/src/ILogger/ApplicationInsightsLoggingBuilderExtensions.cs b/LOGGING/src/ILogger/ApplicationInsightsLoggingBuilderExtensions.cs
index 2a3af65e0f..2b0e813aac 100644
--- a/LOGGING/src/ILogger/ApplicationInsightsLoggingBuilderExtensions.cs
+++ b/LOGGING/src/ILogger/ApplicationInsightsLoggingBuilderExtensions.cs
@@ -34,6 +34,7 @@ public static ILoggingBuilder AddApplicationInsights(this ILoggingBuilder builde
         /// <param name="builder">The <see cref="ILoggingBuilder"/> to use.</param>
         /// <param name="instrumentationKey">Application insights instrumentation key.</param>
         /// <returns>Logging builder with Application Insights added to it.</returns>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use the AddApplicationInsights() overload which accepts Action<TelemetryConfiguration> and set TelemetryConfiguration.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         public static ILoggingBuilder AddApplicationInsights(this ILoggingBuilder builder, string instrumentationKey)
         {
             if (builder == null)
@@ -53,6 +54,7 @@ public static ILoggingBuilder AddApplicationInsights(this ILoggingBuilder builde
         /// <param name="instrumentationKey">Application insights instrumentation key.</param>
         /// <param name="configureApplicationInsightsLoggerOptions">Action to configure ApplicationInsights logger.</param>
         /// <returns>Logging builder with Application Insights added to it.</returns>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use the AddApplicationInsights() overload which accepts Action<TelemetryConfiguration> and set TelemetryConfiguration.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         public static ILoggingBuilder AddApplicationInsights(
             this ILoggingBuilder builder,
             string instrumentationKey,
diff --git a/NETCORE/src/Microsoft.ApplicationInsights.AspNetCore/Extensions/ApplicationInsightsExtensions.cs b/NETCORE/src/Microsoft.ApplicationInsights.AspNetCore/Extensions/ApplicationInsightsExtensions.cs
index 3a47ca39fd..75c43b6dec 100644
--- a/NETCORE/src/Microsoft.ApplicationInsights.AspNetCore/Extensions/ApplicationInsightsExtensions.cs
+++ b/NETCORE/src/Microsoft.ApplicationInsights.AspNetCore/Extensions/ApplicationInsightsExtensions.cs
@@ -43,6 +43,7 @@ public static IApplicationBuilder UseApplicationInsightsExceptionTelemetry(this
         /// <param name="services">The <see cref="IServiceCollection"/> instance.</param>
         /// <param name="instrumentationKey">Instrumentation key to use for telemetry.</param>
         /// <returns>The <see cref="IServiceCollection"/>.</returns>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use the AddApplicationInsightsTelemetry() overload which accepts Action<ApplicationInsightsServiceOptions> and set ApplicationInsightsServiceOptions.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         public static IServiceCollection AddApplicationInsightsTelemetry(
             this IServiceCollection services,
             string instrumentationKey)
diff --git a/NETCORE/src/Microsoft.ApplicationInsights.WorkerService/ApplicationInsightsExtensions.cs b/NETCORE/src/Microsoft.ApplicationInsights.WorkerService/ApplicationInsightsExtensions.cs
index 4790a4e9d3..64776d38b4 100644
--- a/NETCORE/src/Microsoft.ApplicationInsights.WorkerService/ApplicationInsightsExtensions.cs
+++ b/NETCORE/src/Microsoft.ApplicationInsights.WorkerService/ApplicationInsightsExtensions.cs
@@ -21,6 +21,7 @@ public static partial class ApplicationInsightsExtensions
         /// <param name="services">The <see cref="IServiceCollection"/> instance.</param>
         /// <param name="instrumentationKey">Instrumentation key to use for telemetry.</param>
         /// <returns>The <see cref="IServiceCollection"/>.</returns>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use the AddApplicationInsightsTelemetryWorkerService() overload which accepts Action<ApplicationInsightsServiceOptions> and set ApplicationInsightsServiceOptions.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         public static IServiceCollection AddApplicationInsightsTelemetryWorkerService(
             this IServiceCollection services,
             string instrumentationKey)
diff --git a/NETCORE/src/Shared/Extensions/ApplicationInsightsExtensions.cs b/NETCORE/src/Shared/Extensions/ApplicationInsightsExtensions.cs
index be490174a0..1c098c3a96 100644
--- a/NETCORE/src/Shared/Extensions/ApplicationInsightsExtensions.cs
+++ b/NETCORE/src/Shared/Extensions/ApplicationInsightsExtensions.cs
@@ -158,6 +158,7 @@ public static IServiceCollection ConfigureTelemetryModule<T>(
         /// <param name="endpointAddress">Sets telemetry endpoint address.</param>
         /// <param name="instrumentationKey">Sets instrumentation key.</param>
         /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use the AddApplicationInsightsSettings() overload which accepts string ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         [SuppressMessage("ApiDesign", "RS0026:Do not add multiple public overloads with optional parameters", Justification = "We made a mistake here, but we can't remove it from the public API now.")]
         public static IConfigurationBuilder AddApplicationInsightsSettings(this IConfigurationBuilder configurationSourceRoot,  bool? developerMode = null, string endpointAddress = null, string instrumentationKey = null)
             => configurationSourceRoot.AddApplicationInsightsSettings(connectionString: null, developerMode: developerMode, endpointAddress: endpointAddress, instrumentationKey: instrumentationKey);
@@ -246,7 +247,9 @@ internal static void AddTelemetryConfiguration(
 
                 if (config.TryGetValue(primaryKey: InstrumentationKeyForWebSites, backupKey: InstrumentationKeyFromConfig, value: out string instrumentationKey))
                 {
+#pragma warning disable CS0618 // Type or member is obsolete
                     serviceOptions.InstrumentationKey = instrumentationKey;
+#pragma warning restore CS0618 // Type or member is obsolete
                 }
 
                 if (config.TryGetValue(primaryKey: DeveloperModeForWebSites, backupKey: DeveloperModeFromConfig, value: out string developerModeValue))
diff --git a/NETCORE/src/Shared/Extensions/ApplicationInsightsServiceOptions.cs b/NETCORE/src/Shared/Extensions/ApplicationInsightsServiceOptions.cs
index 847ae032f7..ad9a67ea79 100644
--- a/NETCORE/src/Shared/Extensions/ApplicationInsightsServiceOptions.cs
+++ b/NETCORE/src/Shared/Extensions/ApplicationInsightsServiceOptions.cs
@@ -4,6 +4,7 @@ namespace Microsoft.ApplicationInsights.AspNetCore.Extensions
     namespace Microsoft.ApplicationInsights.WorkerService
 #endif
 {
+    using System;
     using System.Reflection;
     using Microsoft.ApplicationInsights.DependencyCollector;
 
@@ -59,6 +60,7 @@ public class ApplicationInsightsServiceOptions
         /// <summary>
         /// Gets or sets the default instrumentation key for the application.
         /// </summary>
+        [Obsolete("InstrumentationKey based global ingestion is being deprecated. Use ApplicationInsightsServiceOptions.ConnectionString. See https://github.com/microsoft/ApplicationInsights-dotnet/issues/2560 for more details.")]
         public string InstrumentationKey { get; set; }
 
         /// <summary>
@@ -161,10 +163,12 @@ internal void CopyPropertiesTo(ApplicationInsightsServiceOptions target)
                 target.EndpointAddress = this.EndpointAddress;
             }
 
+#pragma warning disable CS0618 // Type or member is obsolete
             if (!string.IsNullOrEmpty(this.InstrumentationKey))
             {
                 target.InstrumentationKey = this.InstrumentationKey;
             }
+#pragma warning restore CS0618 // Type or member is obsolete
 
             if (!string.IsNullOrEmpty(this.ConnectionString))
             {
diff --git a/NETCORE/src/Shared/Implementation/TelemetryConfigurationOptionsSetup.cs b/NETCORE/src/Shared/Implementation/TelemetryConfigurationOptionsSetup.cs
index d8d707bcd6..2d98183921 100644
--- a/NETCORE/src/Shared/Implementation/TelemetryConfigurationOptionsSetup.cs
+++ b/NETCORE/src/Shared/Implementation/TelemetryConfigurationOptionsSetup.cs
@@ -72,10 +72,12 @@ public void Configure(TelemetryConfiguration configuration)
         {
             try
             {
+#pragma warning disable CS0618 // Type or member is obsolete
                 if (this.applicationInsightsServiceOptions.InstrumentationKey != null)
                 {
                     configuration.InstrumentationKey = this.applicationInsightsServiceOptions.InstrumentationKey;
                 }
+#pragma warning restore CS0618 // Type or member is obsolete
 
                 if (this.telemetryModuleConfigurators.Any())
                 {
diff --git a/WEB/Src/WindowsServer/WindowsServer/UnhandledExceptionTelemetryModule.cs b/WEB/Src/WindowsServer/WindowsServer/UnhandledExceptionTelemetryModule.cs
index 6d7f2c0055..13db65b126 100644
--- a/WEB/Src/WindowsServer/WindowsServer/UnhandledExceptionTelemetryModule.cs
+++ b/WEB/Src/WindowsServer/WindowsServer/UnhandledExceptionTelemetryModule.cs
@@ -62,7 +62,9 @@ public void Dispose()
 
         private static void CopyConfiguration(TelemetryConfiguration source, TelemetryConfiguration target)
         {
-            target.InstrumentationKey = source.InstrumentationKey;            
+#pragma warning disable CS0618 // Type or member is obsolete
+            target.InstrumentationKey = source.InstrumentationKey;
+#pragma warning restore CS0618 // Type or member is obsolete
 
             foreach (var telemetryInitializer in source.TelemetryInitializers)
             {