During evolution, organisms developed adaptative mechanisms to survive continuous aggressions from a variety of pathogens. Among these lines of defence, many cellular proteins have been described to modulate viral replication and are the subject of intense study. This review will focus on IFITM (interferon induced transmembrane protein), a family of proteins that act against a particularly wide range of viruses. We will summarize our knowledge of the antiviral mechanisms used by IFITM to interfere with the replication of several viruses, and more specifically HIV (human immunodeficiency virus).