A company is a military unit, typically consisting of 100–250 soldiers and usually commanded by a major or a captain. Most companies are formed of three to seven platoons, although the exact number may vary by country, unit type, and structure.
Usually several companies are grouped as a battalion or regiment, the latter of which is sometimes formed by several battalions. Occasionally, independent or separate companies are organized for special purposes, such as the 1st Air Naval Gunfire Liaison Company or the 3rd Force Reconnaissance Company. These companies are not organic to a battalion or regiment, but rather report directly to a higher level organization such as a Marine Expeditionary Force headquarters (i.e., a corps-level command).
The modern military company became popularized during the reorganization of the Swedish Army in 1631 under King Gustav II Adolph. For administrative purposes, the infantry was divided into companies consisting of 150 men, grouped into regiments of eight companies. Tactically, the infantry companies were organized into battalions and grouped with cavalry troops and artillery batteries to form brigades.
From ancient times, some armies have commonly used a base administrative and tactical unit of around 100 men. (Perhaps the best known is the Roman century, originally intended as a 100-man unit, but later ranging from about 60 to 80 men, depending on the time period.) An organization based on the decimal number system (i.e., by tens, hundreds, thousands, and ten-thousands) might seem intuitive. To the Romans, for example, a unit of 100 men seemed sufficiently large to efficiently facilitate organizing a large body of men numbering into the several thousands, yet small enough that one man could reasonably expect to command it as a cohesive unit by using his voice and physical presence, supplemented by musical notes (e.g., drum beats, bugle or trumpet blasts, etc.) and visual cues (e.g., colors, standards, guidons, etc.).