This article describes a tabu search heuristic for the Dial-a-Ride Problem with the following characteristics. Users specify transportation requests between origins and destinations. They may provide a time window on their desired departure or arrival time. Transportation is supplied by a fleet of vehicles based at a common depot. The aim is to design a set of least cost vehicle routes capable of accommodating all requests. Side constraints relate to vehicle capacity, route duration and the maximum ride time of any user. Extensive computational results are reported on randomly generated and real-life data sets.