This document presents a specification for a Basic Execution Service (BES): a service to which clients can send requests to initiate, monitor, and manage computational activities. The specification defines an extensible state model for activities; an extensible information model for a BES and the activities that it creates; and two port-types; BES-Management and BES-Factory. BES-Management defines operations for managing the BES itself. BES-Factory defines operations for initiating, monitoring, and managing sets of activities, and for accessing information about the BES. An optional unspecified BES-Activity port-type indicates an extension point for operations relating to the monitoring and management of individual activities.