This paper deals with the performance prediction of one member of a family of thrust producing intermittent combustion engines, namely the pulsejet.The first part is concerned with formulating basic concepts of how pulsejets work. It describes the different methods of providing intake valving action and derives theory to demonstrate the operation of the aerodynamic tuned valve in particular.The second part is concerned with devising a computer program to simulate and predict the performance of valveless pulsejets. The program is based on the method of characteristics for calculating unsteady gas flow. Theories and techniques are given to handle the major problems associated with this application. These problems include the large range of discontinuous temperature and entropy, flow through an area discontinuity and the calculation of mean thrust.These techniques are incorporated in a computer program, which is successfully used to help with the design of a small valveless pulsejet, which was then built and tested. The duct geometry predicted by the program operates successfully and experimental measurements of pressure variations and mean thrust agree well with those calculated.