The synthesis of heat exchanger networks (HENs) has been a major task in the field of process design. Motivated mainly by the rising energy costs observed over the past few decades, the implementation of HENs provides an effective strategy for energy management in the process industries, thus reducing the process operating costs. Early papers in the field provided only the structure of the heat exchanger network, leaving the detailed design of each unit for a later step. However, more recent papers have reported methods that yield a simultaneous solution of the synthesis of the HEN structure along with a detailed design of the heat exchangers included in such a structure. Pressure drop considerations, a factor neglected in the early papers, are now included as part of the problem formulation. Proper equations for the heat transfer units that relate the pressure drops, the film heat transfer coefficients and the heat exchanger geometry are needed in these formulations. This paper presents a review on the research efforts that have produced synthesis methods for HENs that include the simultaneous detailed design of each heat exchanger unit.