High Quality Content by WIKIPEDIA articles! In mathematics, the uniform boundedness principle or Banach-Steinhaus theorem is one of the fundamental results in functional analysis. Together with the Hahn-Banach theorem and the open mapping theorem, it is considered one of the cornerstones of the field. In its basic form, it asserts that for a family of continuous linear operators (and thus bounded operators) whose domain is a Banach space, pointwise boundedness is equivalent to uniform boundedness in operator norm.