This paper reviews some of the previous research works on direct visualization of water behavior inside proton exchange membrane (PEM) fuel cells using a transparent single cell. Several papers which have employed the method have been selected and summarized, and a comparison between the design of the cell, materials, methods, and visual results are presented. The important aspects, advantages of the method, and a summary on the previous investigations are discussed. Some initial works on transparent PEM fuel cell design using a single serpentine flow-field pattern are described. The results show that the direct visualization via transparent PEM fuel cells could be one potential technique for investigating the water behavior inside the channels and a very promising way forward to provide useful data for validation in PEM fuel cell modeling and simulation.