thumb|right|Four-time [[Origins Award-winning play-by-mail game Starweb]]
A play-by-mail game (also known as a PBM game, PBEM game, turn-based game, turn based distance game, or an interactive strategy game.) is a game played through postal mail, email, or other digital media. Correspondence chess and Go were among the first PBM games. Diplomacy has been played by mail since 1963, introducing a multi-player aspect to PBM games. Flying Buffalo Inc. pioneered the first commercially available PBM game in 1970. A small number of PBM companies followed in the 1970s, with an explosion of hundreds of startup PBM companies in the 1980s at the peak of PBM gaming popularity, many of them small hobby companies—more than 90 percent of which eventually folded. A number of independent PBM magazines also started in the 1980s, including The Nuts & Bolts of PBM, Gaming Universal, Paper Mayhem and Flagship. These magazines eventually went out of print, replaced in the 21st century by the online PBM journal Suspense and Decision.
Play-by-mail games (which became known as turn-based games in the digital age) have a number of advantages and disadvantages compared to other kinds of gaming. PBM games have wide ranges for turn lengths. Some games allow turnaround times of a day or less—even hourly. Other games structure multiple days or weeks for players to consider moves or turns and players never run out of opponents to face. If desired, some PBM games can be played for years. Additionally, the complexity of PBM games can be far beyond that allowed by a board game in an afternoon, and pit players against live opponents in these conditions—a challenge some players enjoy. PBM games allow the number of opponents or teams in the dozens—with some previous examples over a thousand players. PBM games also allow gamers to interact with others globally. Games with low turn costs compare well with expensive board or video games. Drawbacks include the price for some PBM games with high setup and/or turn costs, and the lack of the ability for face-to-face roleplaying. Additionally, for some players, certain games can be overly complex, and delays in turn processing can be a negative.
Play-by-mail games are multifaceted. In their earliest form they involved two players mailing each other directly by postal mail, such as in correspondence chess. Multi-player games, such as Diplomacy or more complex games available today, involve a game master who receives and processes orders and adjudicates turn results for players. These games also introduced the element of diplomacy in which participants can discuss gameplay with each other, strategize, and form alliances. In the 1970s and 1980s, some games involved turn results adjudicated completely by humans. Over time, partial or complete turn adjudication by computer became the norm. Games also involve open- and closed-end variants. Open-ended games do not normally end and players can develop their positions to the fullest extent possible; in closed-end games, players pursue victory conditions until a game conclusion. PBM games enable players to explore a diverse array of roles, such as characters in fantasy or medieval settings, space opera, inner city gangs, or more unusual ones such as assuming the role of a microorganism or a monster.
History
thumb|right|Postcard for international correspondence chess
The earliest play-by-mail games developed as a way for geographically separated gamers to compete with each other using postal mail. Chess and Go are among the oldest examples of this. In these two-player games, players sent moves directly to each other. Multi-player games emerged later: Diplomacy is an early example of this type, emerging in 1963, in which a central game master manages the game, receiving moves and publishing adjudications. According to Shannon Appelcline, there was some PBM play in the 1960s, but not much. For example, some wargamers began playing Stalingrad by mail in this period. these included games such as Nuclear Destruction, which launched in 1970. This began the professional PBM industry in the United States. Professional game moderation started in 1971 at Flying Buffalo which added games such as Battleplan, Heroic Fantasy, Starweb, and others, which by the late 1980s were all computer moderated.
For approximately five years, Flying Buffalo was the single dominant company in the US PBM industry until Schubel & Son entered the field in roughly 1976 with the human-moderated Tribes of Crane. Schubel & Son introduced fee structure innovations which allowed players to pay for additional options or special actions outside of the rules. For players with larger bankrolls, this provided advantages and the ability to game the system. The next big entrant was Superior Simulations with its game Empyrean Challenge in 1978. After Harvey played Flying Buffalo's Nuclear Destruction game in the United States in approximately 1971, Rick Loomis suggested that he run the game in the UK with Flying Buffalo providing the computer moderation. Individual PBM game moderators were plentiful in 1980.
Some players, unhappy with their experiences with Schubel & Son and Superior Simulations, launched their own company—Adventures by Mail—with the game, 'Beyond the Stellar Empire', which became "immensely popular". W.G. Armintrout wrote a 1982 article in The Space Gamer magazine warning those thinking of entering the professional PBM field of the importance of playtesting games to mitigate the risk of failure. By the late 1980s, of the more than one hundred play-by-mail companies operating, the majority were hobbies, not run as businesses to make money. Townsend estimated that, in 1988, there were about a dozen profitable PBM companies in the United States—with an additional few in the United Kingdom and the same in Australia. In 1993, the founder of Flagship magazine, Nick Palmer, stated that "recently there has been a rapid diffusion throughout continental Europe where now there are now thousands of players". In 1992, Jon Tindall stated that the number of Australian players was growing, but limited by a relatively small market base. In a 2002 listing of 182 primarily European PBM game publishers and Zines, Flagship listed ten non-UK entries, to include one each from Austria and France, six from Germany, one from Greece, and one from the Netherlands.
thumb|right|List of PBM Game Ratings from the November–December 1993 issue of Paper Mayhem magazine
PBM games up to the 1980s came from multiple sources: some were adapted from existing games and others were designed solely for postal play. In 1985, Pete Tamlyn stated that most popular games had already been attempted in postal play, noting that none had succeeded as well as Diplomacy. Tamlyn added that there was significant experimentation in adapting games to postal play at the time and that most games could be played by mail. Thus they tended to be more complicated and gravitated toward requiring computer assistance. Flagship began publication in the United Kingdom in October 1983, the month before Gaming Universal's first issue was published in the United States. In the early 1990s, Martin Popp also began publishing a quarterly PBM magazine in Sulzberg, Germany called Postspielbote. The PBM genre's two preeminent magazines of the period were Flagship and Paper Mayhem.
In 1984, the PBM industry created a Play-by-Mail Association. This organization had multiple charter members by early 1985 and was holding elections for key positions. Flying Buffalo Inc. conducted a survey of 167 of its players in 1984. It indicated that 96% of its players were male with most in their 20s and 30s. Nearly half were white collar workers, 28% were students, and the remainder engineers and military.
The 1990s brought changes to the PBM world. In the early 1990s, trending PBM games increased in complexity. In this period, email also became an option to transmit turn orders and results. These are called play-by-email (PBEM) games. Flagship reported in 1992 that they knew of 40 PBM gamemasters on Compuserve. One publisher in 2002 called PBM games "Interactive Strategy Games". Turn around time ranges for modern PBM games are wide enough that PBM magazine editors now use the term "turn-based games". Flagship stated in 2005 that "play-by-mail games are often called turn-based games now that most of them are played via the internet". In the 2023 issues of Suspense & Decision, the publisher used the term "Turn Based Distance Gaming".
In the early 1990s, the PBM industry still maintained some of the player momentum from the 1980s. For example, in 1993, Flagship listed 185 active play-by-mail games. Patrick M. Rodgers also stated in Shadis magazine that the United States had over 300 PBM games. And in 1993, the Journal of the PBM Gamer stated that "For the past several years, PBM gaming has increased in popularity." That year, there were a few hundred PBM games available for play globally.