Companies place significant emphasis on business process identification and optimisation. The main reasons for that can be found in identifying a competitive advantage and providing a rapid response to the changes on the market. For these purposes, business process automation is needed. A significant problem in automated business processes is the absence of formal description of human-process interaction. In this thesis, we defined the concept of task and its role in automated business processes. We described scenarios where users are involved in automated business processes based on human tasks, as well as defined human task lifecycle and the main concepts of human activity. We described the BPEL4People formal language to support user interactions and the WS-HumanTask specification for an abstract description of the human task. We have also modelled a practical business process using BPM tools and captured all concepts of human task as well as presented results from production use.