The torque converter is a very complex turbomachine. Its geometry is highly three-dimensional, the working fluid is viscous oil, and it operates under a wide range of flow conditions. However, its hydrodynamic design technology has advanced very little during the past few decades. The design procedure has been based greatly on the use of the cut-and-try approach. The use of such an approach may satisfy the design requirements in terms of diameter, axial length, and K factor, but it may never lead to an optimized design for any given application. In addition, it has been proven to be too costly and time consuming. The current design tools need to be upgraded in order to significantly advance the hydrodynamic design technology.A review of the technology needs in the areas of internal flow, blade design, and performance is presented. First, the three-dimensional internal flow field and the physical mechanisms of the internal flow losses are described. Secondly, two analyses of a stator blade passage, using potential flow and viscous flow finite element computer codes, are shown. Thirdly, experimental techniques used to obtain internal flow data are discussed. Finally, technology required to develop an accurate performance model Is presented.