Each country may store up to 6 unused missionaries at any time, and these automatically generate into your stockpile according to various factors (listed below). A new missionary can be generated at the beginning of any month. Your country's missionaries are indicated in the status bar across the top of the map screen, by a number located next to a head-and-ruffled-collar icon.
Missionaries are gained or lost according to the following factors; rates are per year:
|+2 to -2||Innovative domestic policy||+2 - 0.4*innovative|
|+0 to +2||State religion|| +0 for Pagan/Confucian/Hindu; +0.5 Reformed/Protestant;|
+1 for Catholic/Orthodox/Muslim/Buddhist; +2 for CRC
The maximum rate is thus 4 missionaries/year, for a completely narrowminded Catholic country. The minimum rate is -2 missionaries/year. It is possible to lose missionaries by having "negative gain". Although negative gain can reduce your stockpile to zero, negative gain cannot create negative missionaries. As with other state agents, the minimum of 0.0 applies.
Missionaries can also be gained or lost by events. However there is only one random event which affects them: Commission of a Cathedral (for Christian countries) or Commission of a Great Mosque (for Muslims), which gives one bonus missionary if the "Build it" choice is selected .