Analytical and numerical tools for modeling microchannel heat sinks are presented, including the most important project parameters. An analytical 1D model, suitable for both design and performance calculations, is first developed under lumped capacitance assumption and resorting to standard correlations for Nu under HI boundary conditions. 2D model extensions are then provided separately for poorly and highly conductive substrates: in the former case axial conduction is neglected; in the latter case the 2D model is modified to include axial conduction by exploiting the results from ID model. This innovative approach provides a significant reduction in computational costs with respect to a conventional 3D model. A 3D model is then developed to evaluate the effects of thermal entrance. Finally, some optimization calculations are performed.