Increasing energy consumption worldwide and environmental concerns about global warming have attracted great interest in the development of renewable and eco-friendly energy technologies. Dye-sensitized solar cells (DSSCs) have attracted considerable attention over the last 25 years since they offer possible low-cost conversion of photovoltaic energy. The sensitizer is the most important component of a DSSC, as it is largely responsible for light harvesting and charge separation, as well as the dye regeneration process. As a result, there have been tremendous research efforts in developing sensitizers. However, many challenges remain, and a deeper understanding of the design rules of DSSC sensitizers is required to obtain efficient and long-term stable DSSCs. The purpose of this review is to discuss recent progress and the rational design criteria used in the structural design of organic dyes and porphyrin photosensitizers for use in DSSCs. The effects of molecular structural engineering on the photophysical and electrochemical properties, photovoltaic parameters, and efficiency of DSSCs are presented.