One of the many applications of multiphase heat-transfer is to be able to predict the temperature of the wall of a boiling surface for a given heat flux or the variation of wall heat flux for a known wall temperature distribution. In this section we focus on the methodology to estimate the wall temperature or the wall heat flux depending on the appropriate boundary condition. We focus on describing the regions of heat transfer, locating the onset of nucleate boiling and finally estimating the wall condition.