In an effort to promote the retention and success of undergraduate students, many universities have established bridge programs. These programs are intended to help students who are talented, but need extra preparation to transition successfully from high school and perform at a college level, and have the goal of ensuring that students will be able to succeed and persist in their programs. The programs vary in size, length, structure, and specific focus, and there are many published papers describing individual programs at different universities and presenting evaluation data that has been collected. However, there is a lack of work comparing these programs or synthesizing the research on them. This paper presents a literature review on bridge programs, with a specific focus on engineering bridge programs. Some of the characteristics that are compared are the length of the programs, their structure, and the topics included. Assessment data that has been collected is also noted, as is the degree to which programs have used that assessment data to inform their programs. The comparisons include both key similarities and major differences between bridge programs, and indicate what best practices are known as well as where there are gaps in knowledge related to bridge programs.