A PBeM is a game played by electronic mail. You can, for example, play chess via e-mail by taking turns exchanging chess moves with your opponent in alternate mail messages. Many games can be played, or modified to be played, by electronic mail.
When we say PBeM at Irony Games, we generally are referring to "role playing" games played via e-mail but the mechanics of war games and strategy-based PBeM's are the same.

Role-playing is assuming a character (role) like an actor does during a play. What turns role playing into a game is that there is no script! You must decide what your character will do in an impromptu fashion and what happens next will be a result of those actions. It's sort of like interactive-theater ...
Role-playing has long been used by lawyers to prepare witnesses for court and by business people to `what-if' possibilities in up-coming negotiations.

How does a PBeM work?

The first and foremost rule is to follow the gamemaster's instructions! In general, a PBEM will go through various a few steps to get going: There will be a call for players, character creation, the GM's approval (and rejection ) of characters ... and, finally, the start of the game.
Most PBEM's, quite naturally, will be played by e-mail; but many use [IRC's] to augment them as well. IRC's allow faster interaction; usually the GM will say up front if IRC's will be used. For the most part, PBeM's are played by exchanging mail.
In some general way, the GM will send a mail note, or public post, to all the players describing the surroundings and current situation. The public post may also contain dialog from non-player characters or summaries of characters' previous actions. If there is some specific information that would only be available to a smaller group or a single player, the GM will send a separate e-mail note to them.
Players in turn, send a reply via e-mail message to the GM and other players that describes what their character does in the given situation. If the action is not visible to all the character (or is, perhaps, a question to the GM) private e-mail will be sent also.
The cycle of e-mail messages is then repeated and you're off and PBEM'ing!