This chapter goes through a list of potential thermal regimes occurring prior to the development of the strike-slip setting or transform margin. These have a strong impact on the thermal regime among all controlling factors. This is due to the fact that the thermal regime affects the host continental lithosphere in many different aspects, such as its thickness, metamorphic reactions, melt formation, rheological zonation, and mechanical behavior. Following a brief summary of basic concepts of heat transport and generation, and heat flow presently observed at the Earth’s surface, the chapter discusses thermal regimes and temperature distribution with depth that can exist in continental lithosphere affected by transform margin formation. It sets the stage for the subsequent evolution, which is strongly dependent on the initial subsurface temperature field. Although this influence progressively diminishes as the transform margin evolves, the knowledge of pre-existing thermal regimes may also help to understand spatial variations along a specific transform margin segment and present-day differences between transform margins.