There are seven types of Missionary, one for each religion in the game (dubbed Buddhist Missionary, Christian Missionary, and so on). A Missionary of a particular type can be built in a city only when either or both of these conditions hold:
- The city has a Monastery of its religion.
- The city has the religion, and the civilization is running the Organized Religion civic.
There is a limit of three Missionaries per religion for each civ. If it already has three either in existence, or in build queues, then it cannot queue any more.
Once built, a Missionary is a normal unit which can move around, see other units, etc. It has one special power: if it gets to a city that does not have its religion, it has its special "spread religion" button become active. If you click this button, the Missionary will attempt to spread its religion to the city. Doing this consumes the Missionary regardless of its failure or success.