diff --git a/reference/gtfs.md b/reference/gtfs.md
index 6709c4c..9e21769 100644
--- a/reference/gtfs.md
+++ b/reference/gtfs.md
@@ -41,6 +41,7 @@ Table Name | GTFS spec | Status | Notes
 [frequencies.txt](#frequenciestxt) | Optional | N/A | 
 [levels.txt](#levelstxt) | Experimental | Included | Provides relative elevation information for stop_ids (including boarding platforms and station entrances) within a parent station.
 [lines.txt](#linestxt) | Experimental | Included | Groups similar routes (such as those which serve the same trunk corridor or bus terminal) for the purpose of customer display.
+[linked_datasets.txt](#linked_datasetstxt) | Experimental | Included | URLs to linked GTFS-realtime datasets: Trip Updates, Vehicle Positions and Service Alerts.
 [multi_route_trips.txt](#multi_route_tripstxt) | Experimental | Included | For trips that travel on more than one route, this file identifies additional routes with which the trip should be associated.
 [pathways.txt](#pathwaystxt) | Experimental | Included | Information and travel times about paths within and out of parent stations, including paths between platforms and to/from station entrances.
 [routes.txt](#routestxt) | Required | Included |
@@ -192,6 +193,18 @@ line_color | Experimental | Included | In systems that have colors assigned to l
 line_text_color | Experimental | Included | This field can be used to specify a legible color to use for text drawn against a background of line_color. The color must be provided as a six-character hexadecimal number, for example, `FFD700`. If no color is specified, the default text color is black (`000000`).
 line_sort_order | Experimental | Included | The `line_sort_order` field can be used to order the lines in a way which is ideal for presentation to customers. It must be a non-negative integer. Lines with smaller `line_sort_order` values should be displayed before lines with larger `line_sort_order` values.
 
+## linked_datasets.txt
+
+Experimental file containing URLs and authentication information for linked GTFS-realtime datasets: Trip Updates, Vehicle Positions and Service Alerts. [Learn more about the proposed linked_datasets extension to GTFS.](https://github.com/google/transit/pull/93)
+
+Field Name | GTFS spec | Status | Notes
+---------- | -------- | ------ | --------
+url | Experimental | Included | Contains the URL to the linked dataset.
+trip_updates | Experimental | Included | Indicates whether the dataset at the specified URL may contain [a `TripUpdate` entity](https://github.com/google/transit/blob/master/gtfs-realtime/spec/en/reference.md#message-tripupdate). Valid values are `0` if the dataset does not contain TripUpdate entities, or `1` if the dataset may contain TripUpdate entities.
+vehicle_positions | Experimental | Included | Indicates whether the dataset at the specified URL may contain [a `VehiclePosition` entity](https://github.com/google/transit/blob/master/gtfs-realtime/spec/en/reference.md#message-vehicleposition). Valid values are `0` if the dataset does not contain VehiclePosition entities, or `1` if the dataset may contain VehiclePosition entities.
+service_alerts | Experimental | Included | Indicates whether the dataset at the specified URL may contain [an `Alert` entity](https://github.com/google/transit/blob/master/gtfs-realtime/spec/en/reference.md#message-alert). Valid values are `0` if the dataset does not contain Alert entities, or `1` if the dataset may contain Alert entities.
+authentication_type | Experimental | Included | Defines the type of authentication required to access the URL. Presently, all included URLs have a value of `0` indicating that no authentication is required.
+
 ## multi_route_trips.txt
 
 Some transit trips serve more than one route. For example, Commuter Rail trips that travel partly on the Lowell Line and partly on the Haverhill Line, or bus trips labeled "Route 62/76" that should be shown on the respective schedules for both Route 62 and Route 76. This applies when a trip serves one route and then the other, but also when the trip serves a unique combination of stops from each route.