Information Systems are fundamental to both the day to day operations and competitiveness of most organisations. As the rate of change in organisations continues to increase this dependency has become more critical. However methods for determining the Information Systems that an organisation needs have not moved forward to reflect these increases in organisational turbulence and new capabilities offered by Information Technology. Strategic Alignment is proposed as a new method for Information Systems Planning which recognises the dynamic role of Information Systems as an agent of change and to enable organisations to model and determine how Information Systems can be exploited to improve and transform Business Strategies. Important innovations in the method are incorporation of feedback to ensure that analysis of the interaction of the Information Systems and Business objects within the model is bidirectional. Also that the development of an Information Systems Plan is a complex process which has to be modular. This enables it to incorporate existing results and information where applicable and to deliver its results incrementally. The Strategic Alignment Method has been developed from extensive research which used the Electricity Supply Industry as the source of information because it was facing immense change after its privatisation. As a result detailed case study material is presented as well as the Strategic Alignment Methodology. Maintenance of an Information Systems Plan is also addressed. Once an Information Systems Plan is produced, its implementation can take a number of years. During this time the changes in Business Strategy and Information Systems capability will change. Strategic Alignment proposes methods that will ensure the ongoing harmonisation of the Strategies during the implementation of the plan. The practical nature of the research is reflected in the Addendum which describes the work that has been done to incorporate Strategic Alignment into ICL's services methodology and to train ICL Consultants in its use.