During the long history of human genome evolution, some gene loci have lost the protein-coding abilities due to various kinds of mutations. These genes are termed pseudogenes that are previously regarded as functional inert. Studies in recent decades, however, have discovered many kinds of functions pseudogenes play both in health and in disease, especially in cancer. In this review, we introduce the origination, classification, identification of pseudogenes, and focus on their roles in cancer pathogenesis. These roles have been categorized into DNA level, RNA level and protein level to make them easier to be understood and remembered. Recent advances in pseudogenes as promising subtyping signature of cancer have also been discussed. We sincerely wish this review to provide a concise and reliable reference for researchers interested in this area. (By Dr. Lu Xiao-Jie, http://jmg.bmj.com/content/early/2014/11/12/jmedgenet-2014-102785 )