The Useful Space Principle, or USP, in the game of contract bridge was first articulated in a series of six articles in The Bridge World, published from November 1980 through April 1981. (The International Bridge Press Association awarded its 1981/1982 award for Best Article or Series on a System or Convention to Jeff Rubens for this series.) The USP is expressed succinctly in The Bridge World glossary as "a partnership's assigning meanings to actions so that the remaining bidding space matches the needs of the auction."
The articles on the USP were the genesis of widely used conventional methods such as Kickback and transfer advances of overcalls. The USP tells bidding theorists that bidding space should be allocated where it is most needed.