The Ceylon Electricity Board (CEB) is under a statutory duty to develop and maintain an efficient, coordinated and economical system of Electricity supply for the whole of Sri Lanka. It is also the duty of the Board to generate or acquire supplies of electricity. The CEB methodically plans its development activities in order to provide reliable, quality electricity to the entire nation at affordable prices. This report, the Long Term Generation Expansion Plan 2006-2020, describes the Generation Expansion Planning Studies carried out by the Transmission and Generation Planning Branch of the Ceylon Electricity Board (CEB) for the period 2006-2020. It includes the existing system, methodology, system demand forecast and future generation expansion plan, investment and implementation plans and recommendations. Moreover, the report recommends the implementation of the least cost generation expansion sequence derived for the base demand forecast case and emphasizes the need to implement the plan to avoid energy shortfalls.