This editorial provides an overview of a Special Issue dedicated to the 9th Conference, Process Integration, Modeling, and Optimization for Energy Saving and Pollution Reduction - PRES 2006. Six papers have been selected and peer-reviewed covering important subjects of heat transfer engineering. These papers' focus is on the recent development of various features of heat transfer equipment design and optimization. This issue of Heat Transfer Engineering is the fifth special journal issue dedicated to selected papers from PRES conferences [1, 2, 3, 4].