Many different methodologies have been proposed in Agent Oriented Software Engineering (AOSE) literature, and the concepts they rely on are different from those adopted when implementing the system. This conceptual gap often creates inconsistencies between specifications and implementation. We propose a metamodel-based approach aims to bridge this gap, resulting in an integrated meta-model that merges the best aspects of four relevant AOSE methodologies (GAIA, Tropos, SODA and PASSI). The meta-model assembly followed a well-defined process: we elicited the requirements for the methodology, identified a set of process fragments, throughly compared the concepts belonging to the various fragments, and finally composed the meta-model.