PBM stands for Play-by-Mail. The basic idea is that instead of meeting your fellow players around a table in the same room, you post your orders for each turn to an impartial moderator. The game moderator (who’s called a GM, for short) processes them along with the other player’s orders and sends you the results, ready for you to brood over before you post your orders back for the following turn.

They can handle a larger number of players than it’s easy to gather for a tabletop game, so you’re not restricted to people nearby and can write your orders at a time that suits you. Games can last longer, too, than is generally convenient in a tabletop session. Indeed, though many PBM games end when appropriate victory conditions have been reached, there are some games (such as this one) that are designed to continue indefinitely. In most PBM games there is a wealth of information and options to think over during the time between receiving your results and sending in your orders for the next turn: most PBM games have considerable depth.

A big difference between PBM games and tabletop games is that for each turn in PBM you usually get individual results which are relevant to your own position, not an overview of the whole game. Therefore it’s often necessary to contact some of the other players in order to swap information, agree on boundaries and to ally for mutual protection - or the opposite! This need to interact between turns is called “diplomacy”; it’s not necessary for all PBM games, but it appeals to many players because it’s a way of making friends who share your interests. PBM is strong on sociability! In addition there will be a quarterly newsletter (at a small charge) where you can insult each other, make announcements and spread rumours.

Some GMs moderate their games wholly by computer, some use computers to assist them (As I do here), while others moderate “by hand”. Each method has its own characteristics. Many of the computer-moderated games are competitive games which will end with a winner, and many of the hand-moderated or computer-assisted games are long lasting, open-ended games.