diff --git a/rest/rest-tests.ts b/rest/rest-tests.ts
index be3887246..26346389f 100644
--- a/rest/rest-tests.ts
+++ b/rest/rest-tests.ts
@@ -31,7 +31,7 @@ client({ path: '/data.json' }).then(function(response) {
     console.log('response: ', response);
 });
 
-client = rest.wrap(mime, { mime: 'application/json' }).wrap(errorCode, { code: 500 });
+client = rest.wrap<mime.Config>(mime, { mime: 'application/json' }).wrap(errorCode, { code: 500 });
 client({ path: '/data.json' }).then(
     function(response) {
         console.log('response: ', response);
@@ -87,6 +87,35 @@ var defaulted = interceptor({
     },
 });
 
+interface KnownConfig {
+    prop: string;
+}
+var knownConfig = interceptor({
+    success: (response: rest.Response, config: KnownConfig) => {
+        console.log(config);
+        return response;
+    },
+});
+
+var transformedConfig = interceptor({
+    init: (config: KnownConfig) => {
+        return config.prop;
+    },
+    success: (response: rest.Response, config: string) => {
+        console.log(config);
+        return response;
+    },
+});
+
+var promiseOrResponse = interceptor({
+    success: (response: rest.Response) => {
+        return response;
+    },
+    error: (response: rest.Response) => {
+        return when(response);
+    },
+});
+
 client = rest
     .wrap(defaultRequest)
     .wrap(hateoas)
@@ -103,4 +132,6 @@ client = rest
     .wrap(xdomain)
     .wrap(xhr)
     .wrap(noop)
-    .wrap(fail);
+    .wrap(fail)
+    .wrap(knownConfig, { prop: 'value' })
+    .wrap(transformedConfig, { prop: 'value' });
diff --git a/rest/rest.d.ts b/rest/rest.d.ts
index d8126b72d..37041e150 100644
--- a/rest/rest.d.ts
+++ b/rest/rest.d.ts
@@ -14,7 +14,7 @@ declare module "rest" {
 	function rest(request: rest.Request): rest.ResponsePromise;
 
 	module rest {
-		export function wrap(interceptor: Interceptor, config?: any): Client;
+		export function wrap<T>(interceptor: Interceptor<T>, config?: T): Client;
 
 		export interface Request {
 			method?: string;
@@ -48,8 +48,8 @@ declare module "rest" {
 			header(headerName: string): when.Promise<any>; // string or string[]
 		}
 
-		export interface Interceptor {
-			(parent?: Client, config?: any): Client;
+		export interface Interceptor<T> {
+			(parent?: Client, config?: T): Client;
 		}
 
 		export interface Client {
@@ -57,7 +57,7 @@ declare module "rest" {
 			(request: Request): ResponsePromise;
 
 			skip(): Client;
-			wrap(interceptor: Interceptor, config?: any): Client;
+			wrap<T>(interceptor: Interceptor<T>, config?: T): Client;
 		}
 
 		export interface Meta {
@@ -71,26 +71,15 @@ declare module "rest/interceptor" {
 	import when = require("when");
 	import rest = require("rest");
 
-	function interceptor(config: interceptor.Config): rest.Interceptor;
-	function interceptor(config: interceptor.PromiseConfig): rest.Interceptor;
+	function interceptor<T, U>(config: interceptor.Config<T, U>): rest.Interceptor<T>;
 
 	module interceptor {
-		// TODO: These two configs should be merged to use union output types.
-
-		interface Config {
-			init?: (config: any) => any;
-			request?: (request: rest.Request, config: any, meta: rest.Meta) => rest.Request;
-			response?: (response: rest.Response, config: any, meta: rest.Meta) => rest.Response;
-			success?: (response: rest.Response, config: any, meta: rest.Meta) => rest.Response;
-			error?: (response: rest.Response, config: any, meta: rest.Meta) => rest.Response;
-		}
-
-		interface PromiseConfig {
-			init?: (config: any) => any;
-			request?: (request: rest.Request, config: any, meta: rest.Meta) => when.Promise<rest.Request>;
-			response?: (response: rest.Response, config: any, meta: rest.Meta) => when.Promise<rest.Response>;
-			success?: (response: rest.Response, config: any, meta: rest.Meta) => when.Promise<rest.Response>;
-			error?: (response: rest.Response, config: any, meta: rest.Meta) => when.Promise<rest.Response>;
+		interface Config<T, U> {
+			init?: (config: T) => U;
+			request?: (request: rest.Request, config: U, meta: rest.Meta) => rest.Request | when.Promise<rest.Request>;
+			response?: (response: rest.Response, config: U, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
+			success?: (response: rest.Response, config: U, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
+			error?: (response: rest.Response, config: U, meta: rest.Meta) => rest.Response | when.Promise<rest.Response>;
 		}
 	}
 
@@ -100,7 +89,18 @@ declare module "rest/interceptor" {
 declare module "rest/interceptor/defaultRequest" {
 	import rest = require("rest");
 
-	var defaultRequest: rest.Interceptor;
+	var defaultRequest: rest.Interceptor<defaultRequest.Config>;
+
+	module defaultRequest {
+		interface Config {
+			method?: string;
+			path?: string;
+			params?: any;
+			headers?: any;
+			entity?: any;
+			mixin?: any;
+		}
+	}
 
 	export = defaultRequest;
 }
@@ -108,7 +108,14 @@ declare module "rest/interceptor/defaultRequest" {
 declare module "rest/interceptor/hateoas" {
 	import rest = require("rest");
 
-	var hateoas: rest.Interceptor;
+	var hateoas: rest.Interceptor<hateoas.Config>;
+
+	module hateoas {
+		interface Config {
+			target?: string;
+			client?: rest.Client;
+		}
+	}
 
 	export = hateoas;
 }
@@ -116,15 +123,32 @@ declare module "rest/interceptor/hateoas" {
 declare module "rest/interceptor/location" {
 	import rest = require("rest");
 
-	var location: rest.Interceptor;
+	var location: rest.Interceptor<location.Config>;
+
+	module location {
+		interface Config {
+			client?: rest.Client;
+			code?: number;
+		}
+	}
 
 	export = location;
 }
 
 declare module "rest/interceptor/mime" {
 	import rest = require("rest");
+	import registry = require("rest/mime/registry");
 
-	var mime: rest.Interceptor;
+	var mime: rest.Interceptor<mime.Config>;
+
+	module mime {
+		interface Config {
+			mime?: string;
+			accept?: string;
+			registry?: registry.Registry;
+			permissive?: boolean;
+		}
+	}
 
 	export = mime;
 }
@@ -132,7 +156,13 @@ declare module "rest/interceptor/mime" {
 declare module "rest/interceptor/pathPrefix" {
 	import rest = require("rest");
 
-	var pathPrefix: rest.Interceptor;
+	var pathPrefix: rest.Interceptor<pathPrefix.Config>;
+
+	module pathPrefix {
+		interface Config {
+			prefix?: string;
+		}
+	}
 
 	export = pathPrefix;
 }
@@ -140,7 +170,14 @@ declare module "rest/interceptor/pathPrefix" {
 declare module "rest/interceptor/basicAuth" {
 	import rest = require("rest");
 
-	var basicAuth: rest.Interceptor;
+	var basicAuth: rest.Interceptor<basicAuth.Config>;
+
+	module basicAuth {
+		interface Config {
+			username?: string;
+			password?: string;
+		}
+	}
 
 	export = basicAuth;
 }
@@ -148,7 +185,23 @@ declare module "rest/interceptor/basicAuth" {
 declare module "rest/interceptor/oAuth" {
 	import rest = require("rest");
 
-	var oAuth: rest.Interceptor;
+	var oAuth: rest.Interceptor<oAuth.Config>;
+
+	module oAuth {
+		interface DismissWindow {
+			(): void;
+		}
+		interface Config {
+			token?: string;
+			clientId?: string;
+			scope?: string;
+			authorizationUrl?: string;
+			redirectUrl?: string;
+			windowStrategy?: (url: string) => DismissWindow;
+			oAuthCallback?: (hash: string) => void;
+			oAuthCallbackName?: string;
+		}
+	}
 
 	export = oAuth;
 }
@@ -156,7 +209,14 @@ declare module "rest/interceptor/oAuth" {
 declare module "rest/interceptor/csrf" {
 	import rest = require("rest");
 
-	var csrf: rest.Interceptor;
+	var csrf: rest.Interceptor<csrf.Config>;
+
+	module csrf {
+		interface Config {
+			name?: string;
+			token?: string;
+		}
+	}
 
 	export = csrf;
 }
@@ -164,7 +224,13 @@ declare module "rest/interceptor/csrf" {
 declare module "rest/interceptor/errorCode" {
 	import rest = require("rest");
 
-	var errorCode: rest.Interceptor;
+	var errorCode: rest.Interceptor<errorCode.Config>;
+
+	module errorCode {
+		interface Config {
+			code?: number;
+		}
+	}
 
 	export = errorCode;
 }
@@ -172,7 +238,15 @@ declare module "rest/interceptor/errorCode" {
 declare module "rest/interceptor/retry" {
 	import rest = require("rest");
 
-	var retry: rest.Interceptor;
+	var retry: rest.Interceptor<retry.Config>;
+
+	module retry {
+		interface Config {
+			initial?: number;
+			multiplier?: number;
+			max?: number;
+		}
+	}
 
 	export = retry;
 }
@@ -180,7 +254,14 @@ declare module "rest/interceptor/retry" {
 declare module "rest/interceptor/timeout" {
 	import rest = require("rest");
 
-	var timeout: rest.Interceptor;
+	var timeout: rest.Interceptor<timeout.Config>;
+
+	module timeout {
+		interface Config {
+			timeout?: number;
+			transient?: boolean;
+		}
+	}
 
 	export = timeout;
 }
@@ -188,7 +269,17 @@ declare module "rest/interceptor/timeout" {
 declare module "rest/interceptor/jsonp" {
 	import rest = require("rest");
 
-	var jsonp: rest.Interceptor;
+	var jsonp: rest.Interceptor<jsonp.Config>;
+
+	module jsonp {
+		interface Config {
+			callback?: {
+				param?: string;
+				prefix?: string;
+				name?: string;
+			}
+		}
+	}
 
 	export = jsonp;
 }
@@ -196,7 +287,7 @@ declare module "rest/interceptor/jsonp" {
 declare module "rest/interceptor/ie/xdomain" {
 	import rest = require("rest");
 
-	var xdomain: rest.Interceptor;
+	var xdomain: rest.Interceptor<{}>;
 
 	export = xdomain;
 }
@@ -204,7 +295,7 @@ declare module "rest/interceptor/ie/xdomain" {
 declare module "rest/interceptor/ie/xhr" {
 	import rest = require("rest");
 
-	var xhr: rest.Interceptor;
+	var xhr: rest.Interceptor<{}>;
 
 	export = xhr;
 }
@@ -212,12 +303,19 @@ declare module "rest/interceptor/ie/xhr" {
 declare module "rest/mime/registry" {
 	import when = require("when");
 
-	export interface MIMEConverter {
-		read(value: string): any; // any or when.Promise<any>;
-		write(value: any): any; // string or when.Promise<string>;
+	var registry: registry.Registry;
+
+	module registry {
+		interface MIMEConverter {
+			read(value: string): any | when.Promise<any>;
+			write(value: any): string | when.Promise<string>;
+		}
+
+		interface Registry {
+			lookup(mimeType: string): when.Promise<MIMEConverter>;
+			register(mimeType: string, converter: MIMEConverter): void;
+		}
 	}
 
-	export function lookup(mimeType: string): when.Promise<MIMEConverter>;
-
-	export function register(mimeType: string, converter: MIMEConverter): void;
+	export = registry;
 }