The technical and financial success of a microprocessor based design project can be profoundly influenced by the performance of the development system. This paper reviews types of system commonly in use today, and establishes some approximate measures of performance. Then follows a review of the features and facilities which a good, stand-alone system should include, i.e. texteditor, assembler, linker, debugger, in-circuit emulation and logic analyser, including a brief discussion of different ways of implementing some of these features and the consequent impact on system performance. Finally an attempt is made to establish criteria whereby the performance of a development system may be evaluated in terms of its intended application.