A regiment is a military unit, made up of a number of battalions, run by a Colonel. A modern regiment can also be similar to a brigade, in that both can be from a few hundred soldiers to 5,000 soldiers (from 3 to 7 battalions). The modern regiment's size changes in number, purpose, and role from country to country (and might not exist in some military forces) and sometimes even within the military of the same nations.