Subcooled flow boiling covers the region beginning from the location where the wall temperature exceeds the local liquid saturation temperature to the location where the thermodynamic quality reaches zero, corresponding to the saturated liquid state. Three locations in the subcooled flow have been identified by earlier investigators as the onset of nucleate boiling, the point of net vapor generation, and the location where x = 0 is attained from enthalpy balance equations. The heat transfer regions are identified as the single phase heat transfer prior to ONB, partial boiling (PB), and fully developed boiling (FDB). A new region is identified here as the significant void flow (SVF) region. Available models for predicting the heat transfer coefficient in different regions are evaluated and new models are presented based on our current understanding. The results are compared with some of the experimental data available in the literature.