This paper presents the facilities offered by a new system intended for general thermal analysis and design. THETA consists of a suite of fourteen integrated programs which cover all aspects of problem definition, editing, solution and output processing. They represent a significant departure from earlier programs, taking full advantage of the advances in hardware performance and offering new features such as automated model optimisation and comprehensive self-checking to advise the user of potential errors. It also advises the user if the choice of model discretisation is a poor one. It is being made available on an increasing range of hardware and experience has shown that its use is easily learnt by non-specialists.