StAC (Structured Activity Compensation) is a business process modelling language and distinctive feature of this language is its support for compensation. A compensation is an action taken to recover from error or cope with a change of plan, especially when rollback of a process is not possible. StAC is similar to a process algebraic language such as Hoare's CSP or Milner's CCS but has additional operators dealing with compensation and with exception handling. This talk presents the StAC language and discusses its operational semantics.