This paper presents a survey on the Vehicle Routing Problem with Pickup and Delivery in which a heterogeneous vehicle fleet based at multiple terminals must satisfy a set of transportation requests. Each request is defined by a pickup point, a corresponding delivery point and a demand to be transported between these locations. The requested transport could involve goods or persons. Problems in this class involve time constraints establishing time intervals during which service must take place at each stop, or expressing user inconvenience, and maximum ride time restrictions for passengers.