diff --git a/src/Packages/Audience/Runtime/AudienceConfig.cs b/src/Packages/Audience/Runtime/AudienceConfig.cs
new file mode 100644
index 000000000..759645562
--- /dev/null
+++ b/src/Packages/Audience/Runtime/AudienceConfig.cs
@@ -0,0 +1,17 @@
+namespace Immutable.Audience
+{
+    /// <summary>Configuration passed to <see cref="ImmutableAudience.Init"/>.</summary>
+    public class AudienceConfig
+    {
+        public string PublishableKey { get; set; }
+        public ConsentLevel Consent { get; set; } = ConsentLevel.None;
+        /// <summary>
+        /// Distribution platform the game is running on.
+        /// Use <see cref="DistributionPlatforms"/> for common values, or pass any custom string.
+        /// </summary>
+        public string DistributionPlatform { get; set; }
+        public bool Debug { get; set; } = false;
+        public int FlushIntervalSeconds { get; set; } = Constants.DefaultFlushIntervalSeconds;
+        public int FlushSize { get; set; } = Constants.DefaultFlushSize;
+    }
+}
diff --git a/src/Packages/Audience/Runtime/AudienceConfig.cs.meta b/src/Packages/Audience/Runtime/AudienceConfig.cs.meta
new file mode 100644
index 000000000..ab5d113be
--- /dev/null
+++ b/src/Packages/Audience/Runtime/AudienceConfig.cs.meta
@@ -0,0 +1,11 @@
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diff --git a/src/Packages/Audience/Runtime/AudienceError.cs b/src/Packages/Audience/Runtime/AudienceError.cs
new file mode 100644
index 000000000..3e57ada0b
--- /dev/null
+++ b/src/Packages/Audience/Runtime/AudienceError.cs
@@ -0,0 +1,23 @@
+using System;
+
+namespace Immutable.Audience
+{
+    public enum AudienceErrorCode
+    {
+        FlushFailed,
+        ValidationRejected,
+        ConsentSyncFailed,
+        NetworkError
+    }
+
+    public class AudienceError : Exception
+    {
+        public AudienceErrorCode Code { get; }
+
+        public AudienceError(AudienceErrorCode code, string message)
+            : base(message)
+        {
+            Code = code;
+        }
+    }
+}
diff --git a/src/Packages/Audience/Runtime/AudienceError.cs.meta b/src/Packages/Audience/Runtime/AudienceError.cs.meta
new file mode 100644
index 000000000..b1b7d9574
--- /dev/null
+++ b/src/Packages/Audience/Runtime/AudienceError.cs.meta
@@ -0,0 +1,11 @@
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diff --git a/src/Packages/Audience/Runtime/ConsentLevel.cs b/src/Packages/Audience/Runtime/ConsentLevel.cs
new file mode 100644
index 000000000..66e518c05
--- /dev/null
+++ b/src/Packages/Audience/Runtime/ConsentLevel.cs
@@ -0,0 +1,13 @@
+namespace Immutable.Audience
+{
+    /// <summary>Controls what the Audience SDK tracks.</summary>
+    public enum ConsentLevel
+    {
+        /// <summary>SDK inert. No events queued or sent. No IDs persisted to disk.</summary>
+        None,
+        /// <summary>Track events with anonymousId only. Identify/Alias discarded with warning.</summary>
+        Anonymous,
+        /// <summary>All events. Identify/Alias send. userId attached to track events.</summary>
+        Full
+    }
+}
diff --git a/src/Packages/Audience/Runtime/ConsentLevel.cs.meta b/src/Packages/Audience/Runtime/ConsentLevel.cs.meta
new file mode 100644
index 000000000..4f6dee409
--- /dev/null
+++ b/src/Packages/Audience/Runtime/ConsentLevel.cs.meta
@@ -0,0 +1,11 @@
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diff --git a/src/Packages/Audience/Runtime/Core.meta b/src/Packages/Audience/Runtime/Core.meta
new file mode 100644
index 000000000..e353cf31f
--- /dev/null
+++ b/src/Packages/Audience/Runtime/Core.meta
@@ -0,0 +1,8 @@
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diff --git a/src/Packages/Audience/Runtime/Core/Constants.cs b/src/Packages/Audience/Runtime/Core/Constants.cs
new file mode 100644
index 000000000..6573730d8
--- /dev/null
+++ b/src/Packages/Audience/Runtime/Core/Constants.cs
@@ -0,0 +1,40 @@
+namespace Immutable.Audience
+{
+    internal static class Constants
+    {
+        internal const string TestKeyPrefix = "pk_imapik-test-";
+        internal const string SandboxBaseUrl = "https://api.sandbox.immutable.com";
+        internal const string ProductionBaseUrl = "https://api.immutable.com";
+
+        internal const string MessagesPath = "/v1/audience/messages";
+        internal const string ConsentPath = "/v1/audience/tracking-consent";
+        internal const string DataPath = "/v1/audience/data";
+
+        internal const int DefaultFlushIntervalSeconds = 5;
+        internal const int DefaultFlushSize = 20;
+        internal const int MaxBatchSize = 100;
+        internal const int StaleEventDays = 30;
+
+        internal const string LibraryName = "com.immutable.audience";
+        internal const string Surface = "unity";
+        internal const string ConsentSource = "UnitySDK";
+
+        internal static string BaseUrl(string publishableKey) =>
+            publishableKey != null && publishableKey.StartsWith(TestKeyPrefix)
+                ? SandboxBaseUrl
+                : ProductionBaseUrl;
+    }
+
+    /// <summary>
+    /// String constants for common game distribution platforms.
+    /// Any string is accepted -- studios are not limited to these values.
+    /// </summary>
+    public static class DistributionPlatforms
+    {
+        public const string Steam = "steam";
+        public const string Epic = "epic";
+        public const string GOG = "gog";
+        public const string Itch = "itch";
+        public const string Standalone = "standalone";
+    }
+}
diff --git a/src/Packages/Audience/Runtime/Core/Constants.cs.meta b/src/Packages/Audience/Runtime/Core/Constants.cs.meta
new file mode 100644
index 000000000..d222e9aa5
--- /dev/null
+++ b/src/Packages/Audience/Runtime/Core/Constants.cs.meta
@@ -0,0 +1,11 @@
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diff --git a/src/Packages/Audience/Runtime/ImmutableAudience.cs b/src/Packages/Audience/Runtime/ImmutableAudience.cs
index 677c80370..6c882b7b7 100644
--- a/src/Packages/Audience/Runtime/ImmutableAudience.cs
+++ b/src/Packages/Audience/Runtime/ImmutableAudience.cs
@@ -2,11 +2,17 @@ namespace Immutable.Audience
 {
     /// <summary>
     /// Entry point for the Immutable Audience SDK.
-    /// Call Init once on startup, then use the static methods from any thread.
+    /// Call <see cref="Init"/> once on startup, then use the static methods from any thread.
     /// </summary>
     public static class ImmutableAudience
     {
-        // Core types (AudienceConfig, ConsentLevel, AudienceError) and Init
-        // are added in the next PR once those types exist. See SDK-119.
+        // Scaffold only -- implementation follows in subsequent sub-issues (see SDK-99).
+
+        /// <summary>Initialise the SDK. Call once, typically in your game's entry scene.</summary>
+        public static void Init(AudienceConfig config)
+        {
+            throw new System.NotImplementedException(
+                "Immutable Audience SDK: implementation pending. See SDK-99.");
+        }
     }
 }
diff --git a/src/Packages/Audience/Runtime/ImmutableAudience.cs.meta b/src/Packages/Audience/Runtime/ImmutableAudience.cs.meta
index 6e249f726..bf98375d9 100644
--- a/src/Packages/Audience/Runtime/ImmutableAudience.cs.meta
+++ b/src/Packages/Audience/Runtime/ImmutableAudience.cs.meta
@@ -1,5 +1,5 @@
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