MilSim includes activities that strive to provide an experience of combat, simulate battlefield missions, or replicate military service-style training.

There are several forms of MilSim: physical shooting sports (e.g. airsoft, paintball, or laser tag) with an emphasis on realism based on military scenarios and team tactics; historical reenactment of famous battles; stylistic imitations of a specific military era or focus, such as cosplaying; and military-themed e-sports (e.g. video games).

Airsoft guns are used commonly in MilSim due to their cosmetic realism, satisfactory external ballistics, compatibility with genuine firearm accessories, and inexpensive ammunition.

Events can span between historical or imaginary battles, law enforcement-style CQC engagements, or freestyle urban/jungle warfare-themed light infantry skirmishes.

In the United Kingdom, airsoft organizers run in conjunction with Live Action Role-Players (LARP) at British Army training facilities, such as Copehill Down and Catterick Garrison.

[1] Regularly, military veterans from several nations will attend or organize events, giving further accuracy to first-aid training, current terminology, clothing, and tactics.

Robert Silverman of Vocativ, embedded in a two-day MilSim (inspired by 2003's Tears of the Sun), writes that "the appeal is in ... the realism of an unreal world, plus a deep desire for the camaraderie and teamwork you'd find in a real military unit."

He speculates that the "pure adrenaline free from inflicting actual harm ... strikes at something embedded deep within the core of sports.

Games such as Arma and Squad rather than pure entertainment, are a simulation of equipment and tactics, and are sometimes used for military training and mission rehearsal.