Vaccination programs are an important component of public health initiatives and preventative medicine. This is particularly true in an urban environment where such factors as density, sanitation and pollution increase exposure to a variety of communicable disease. The most vulnerable populations such as slum-dwelling poor, homeless individuals and the elderly-poor are both more prone to exposure to communicable disease and to having a more limited access to the receipt of appropriate vaccinations to prevent them. A variety of programs have been utilized to maximize delivery of important vaccines to homeless individuals. Monetary incentives, education and ease of access are components of some of the more successful vaccination programs. This paper will provide a literature review of barriers to vaccination in homeless populations, programs and initiatives as well as future directions for vaccination programs.