As a discipline, engineering thermodynamics is concerned with traditional and alternative sources of energy in terms of availability, movement and conversion. Practical issues such as efficiency of thermodynamic processes and systems are also studied. Stout understanding of thermodynamics by graduating engineers is indispensable for addressing the foremost global issue: the looming energy crisis and its related problems of pollution and global warming. Despite this monumental importance, engineering students continue to struggle with thermodynamics as indicated by the results of recent national US exams. Student's difficulties with thermodynamics have been also reported in several European countries, Australia and India. The current authors contend that understanding the root causes of problems with teaching/learning thermodynamics is an indispensable first step toward a design of an instructional strategy (and/or curricula and textbooks) geared at removing barriers to students' learning of thermodynamics. The purpose of this paper is to give a concise yet comprehensive account of the pertinent literature, and to analyze this literature in order to accurately describe the nature of problems of learning and teaching thermodynamics. The paper also describes the methods used for probing these problems, tried techniques for solving them and the degree of success achieved. In general, the literature points at two challenging problems. First, students do not properly learn thermodynamic concepts and principles; second, students have difficulty recognizing relevant concepts and principles, and putting them together in order to solve thermodynamic problems. The latter problem seems to not have received vital study and attention as the former. More details about these problems are given in this paper.