The Culbertson 4-5 notrump is a slam-seeking convention in the game of contract bridge. It was devised in the early 1930s by Ely Culbertson. Most four-notrump conventions (Blackwood and its variants being the best known) demand that bidder's partner define their hand using agreed codified responses. In contrast, the Culbertson 4-5 describes the bidder's hand, and invites partner to use their judgement in the light of that information.[1]