  The topic of this review is the current state of our knowledge about the
degree of initial equilibration between electrons, protons and ions at
supernova remnant (SNR) shocks. Specifically, the question has been raised as
to whether there is an inverse relationship between the shock velocity and the
equilibration similar to the relationship between equilibration and Alfven Mach
number seen in interplanetary shocks (Schwartz et al 1988). This review aims to
compile every method that has been used to measure the equilibration and every
SNR on which they have been tested. I review each method, its problems and
uncertainties and how those would effect the degree of equilibration (or
velocity) inferred. The final compilation of observed electron to proton
temperature ratios as a function of shock velocity gives an accurate,
conservative picture of the state of our knowledge and the avenues we need to
pursue to make progress in our understanding of the relation between the
velocity of a shock and the degree of equilibration.
