From Citizendium, the Citizens' Compendium
In many armies, such the United States, a brigadier general (BG) is the lowest grade of general officer. Armies on the Commonwealth pattern call the rank brigadier, and consider it the highest field-grade rank, senior to a colonel but not a general rank. Yet other armies on the Russian pattern do not use the rank at all, going directly from colonel to major general.
It is not always easy to characterize the responsibility associated with the rank. Seemingly contradicting the title, brigade combat teams (BCT) and support brigades are commanded by colonels. A U.S. Marine Amphibious Brigade (MAB) does have a Marine BG in command; but a MAB is larger than a BCT, having significant aircraft and support components as well as a ground component, based on a reinforced Marine regiment comparable in size to an Army infantry BCT. U.S. Army brigadier generals tend to be deputy division commanders, senior staff officers, or leading large task forces.
The rank is often called "one-star" after the U.S. designation. This becomes even more confusing when compared to naval ranks; a commodore may be simply the senior captain (naval) of a unit, a one-star flag officer, or the navy may not use the title at all. When the "commodore" title is not used, the navy may have two grades called rear admiral, sometimes both wearing two stars or the equivalent insignia even though the "rear admirals of the lower half" are of the same level of authority of a brigadier or brigadier general. It is sometimes suggested that this is not to confuse enemy countries, but to infuriate the true opponents: the navy and army of the country under discussion.
The Israeli Defense Forces has a rather lower rank structure than other militaries, including many a good deal less powerful. There is a single lieutenant general commanding the entire Israeli Defense Forces, with major generals in divisional/regional and key staff positions, as well as commanding their noted air force. Brigadiers are, however, considered general officers.
During the Vietnam War, a corps in the Army of the Republic of Viet Nam was a regional rather than a tactical level of organization, and might well be commanded by a brigadier general, although the rank could be higher.