The current study aimed to conduct a literature review on the subject of identifier names in computer programs. Specifically, this review focused on three research topics: identifier structure and their semantics, identifier quality measures, and how developers choose names. This review included 33 papers extending from 1998 to 2021. Key findings suggest that lexicon quality and structure greatly impact developer cognition and performance, which translates to overall quality of software, as well as speed with which it is created. However, tools, methods and naming guidelines that improve the code lexicon are rarely applied commercially. Finally, future research is needed to develop a complete theory of program comprehension to understand the role of identifiers in the process.