The Tsukuba Express (つくばエクスプレス線, Tsukuba Ekusupuresu-sen^?), or TX, is a Japanese railway line of the Metropolitan Intercity Railway Company which links Akihabara Station in Chiyoda, Tokyo and Tsukuba Station in Tsukuba, Ibaraki. The route was inaugurated on August 24, 2005.

Initially, the line was to be called Jōban Shinsen (New Jōban Line). The reason for the line was to relieve crowding on the Jōban Line of East Japan Railway Company (JR East), which had reached the limit of its capacity. However, with the economic downturn in Japan, the goal shifted to development along the line. Also, the initial plan called for a line from Tokyo to Moriya, but expenses forced the planners to start the line at Akihabara instead of Tokyo, and pressure from the government of Ibaraki Prefecture resulted in moving the extension from Moriya to Tsukuba into Phase I of the construction.

The original schedule called for the line to begin operating in 2000, but delays resulted in a 2005 start.

The line has a top speed of 130 km/h. Rapid service has reduced the time required for the trip from Akihabara to Tsukuba from the previous 1 hour 30 minutes (by the Jōban Line, arriving in Tsuchiura, about 15 km from Tsukuba) or 70 minutes (by bus, under optimal traffic conditions) to 45 minutes; from Tokyo, the trip requires 50 – 55 minutes. The line has no grade crossings.