Computers have gone from being solely large number crunching machines to small devices capable of performing a myriad of functions in a very small space of time. Computers are now used to control just about every facet of daily life; they can now be found in automobiles, washing machines and home heating systems. This rapid diversification brings a great many problems. Traditional software engineering methodologies are failing to meet and address these new problems. The goal of this thesis is to develop a new approach to organisational requirements engineering. A new modelling approach to representing organisations will be developed which will draw upon the concepts of a systems architecture, modelling the life cycle of responsibilities and the execution of conversations. Using this architecture an organisation will be able to embed social and cultural aspects within the modelling notation. From the modelling of responsibilities a clearer picture of the organisation's aims, objectives and policies will be developed along with a definition of what objects and access rights are required in order for the organisation to function. Using speech act and Petri net based models to model conversations a clearer understanding of the dynamics and constraints governing organisational behaviour can be developed. These modelling approaches are then applied to two real life case studies in order to demonstrate and evaluate their performance and usefulness.