The work presented in this report is concerned with the passive control of power and loads on horizontal axis wind turbines. A review of machines which use passive control techniques is presented along with an exploration of their success or failure in practice. A mathematical model of a wind turbine has been constructed and each of the possible ways to use the forces acting on the wind turbine has been investigated in a systematic manner. In this way a very broad range of possible passive control schemes has been considered. These include methods which use passive pitching to both stall and fine pitch. blade coning and drive train flexibility. Both fixed speed and variable speed operation have been considered. The characteristics of the power control and of loads at the rotor and the drive train have been established. These have been compared with those for a typical active pitch controlled machine. Static and dynamic characteristics have been considered. An assessment of the likely complexity of each type of system has been made. This is compared to the complexity inherent in an active, pitch controlled machine and a stall regulated machine. (author).