In this book our objective is to explain different types of Plate-Fin Heat Exchanger, and typical method of design and optimization of them.Compact heat exchangers are generally characterized by extended surfaces with large surface area /volume rations that are often configured in either plate-fin or tube-fin arrangements. Depending on the application ,various types of argumented heat exchanger surfaces such as plain fins ,wavy fins ,offset strip fins , louvered fins and perforated fins are used .Due to use fins on both sides to interrupt boundary layer growth ,plate-fin heat exchanger has high effectiveness and high thermal conductivity. Thus ,this can lead to reduction of space requirement ,energy consumption ,weight and cost. However , there is of course ,an associated growth in the pressure drop owing to increased friction .Therefore ,the optimum design of compact heat exchanger is always required as the optimal trade-off between the increased heat transfer rate and power consumption due to higher pressure drop within the given seat of constraints .