In the partnership card game contract bridge, the Blackwood convention is a bidding convention developed by Easley Blackwood in 1933[1] and still widely used in the modern game. Its purpose is to enable the partnership to explore its possession of aces, kings and in some variants, the queen of trumps to judge whether a slam would be a feasible contract. The essence of the convention is the use of an artificial 4NT bid made under certain conditions to ask partner how many aces he has; responses by partner are made in step-wise fashion to indicate the number held.