The Search for Extraterrestrial Intelligence (SETI) is the collective name for a number of activities people undertake to search for intelligent extra-terrestrials life. Some of the most well known projects are run by the SETI Institute. SETI projects use scientific methods to search for intelligent life on other planets. For example, electromagnetic radiation is monitored for signs of transmissions from civilizations on other worlds. The United States government contributed to early SETI projects, but recent work has been primarily funded by private sources.

There are great challenges in searching across the cosmos for a first transmission that could be characterized as intelligent, since its direction, spectrum and method of communication are all unknown beforehand. SETI projects necessarily make assumptions to narrow the search, the foremost being that electromagnetic radiation would be a medium of communication for advanced extra-terrestrial life.