The DNA mismatch repair (MMR) pathway is one of the most critical genome surveillance systems for governing faithful transmission of genetic information during DNA replication. The functional necessity of this pathway in humans is partially reflected by the tight link between MMR gene mutations and the development of hereditary nonpolyposis colorectal cancer. Increasing evidence has suggested a broad involvement of MMR proteins in various aspects of DNA metabolism beyond the scope of DNA mismatch correction, such as in the processes of DNA damage response and homologous recombination. Though evidence is presently lacking for potential functional involvement of hMSH4 and hMSH5 in MMR, these two proteins are thought to play roles in meiotic and mitotic DNA double strand break (DSB) repair and DNA damage responses in human cells.