Thermodynamics is defined as the science of energy and entropy which are applicable to all fields of science and engineering. This special issue is essentially devoted to the entropy generation in thermal engineering systems and applications. Entropy generation is one of the most significant problems to overcome to optimize a system/process and its performance, and this will unfortunately remain as a crucial problem to the next generation. In this regard, better understanding of the concept of entropy and its role amo ng various classes of thermal systems and processes with a diverse coverage is crucial. Research into transport phenomena in energy systems and applications has substantially increased during the past a few decades due to its diversity in applications. This makes the special issue a most timely addition to existing literature. It includes recent major developments in both the fundamental and applications, and provides a valuable source to researchers dealing with analysis of entropy generation in thermal systems and processes. This special issue contains 14 technical papers on entropy generation in thermal systems and processes ranging from heat engines to natural/forced convection systems. The collection of topic included is suitable for a wide range of interests from practitioners to researchers working on thermal systems and processes. Each paper was peer-reviewed under the guidelines of the Journal before publication.