Holonic multiagent systems (HMAS) offers a promising software engineering approach for developing complex open software systems. However the process of building MultiAgent Systems (MAS) and HMAS is mostly different from the process of building more traditional software systems and it introduces new design and development challenges. This paper introduces an agent-oriented software process for engineering complex systems called ASPECS. ASPECS is based on a holonic organisational metamodel and provides a step-by-step guide from requirements to code allowing the modelling of a system at different levels of details using a suite of refinement methods. Keywords : Agent Oriented Software Engineering