~Basic Blackwood and Gerber

There are two basic conventions used to ask for aces and kings:

Blackwood: over a suit bid, 4NT is commonly used to ask for aces. Responses are
~5C–0 or 4 aces
~5D–1 ace
~5H–2 aces
~5S–3 aces

The 4NT bidder may now ask for kings by bidding 5NT. The bid shows that the partnership holds all the aces. Responses are
~6C–0 or 4 kings
~6D–1 king
~6H–2 kings
~6S–3 kings

Gerber: a bid of 4C generally used immediately after a NT bid to ask for aces. Responses are
~4D–0 or 4 aces
~4H–1 ace
~4S–2 aces
~4NT–3 aces

The 4C bidder may now ask for kings by bidding 5C. The 5C bid need not promise that the partnership holds all the aces, as it is possible to stop at 5NT. Responses are
~5D–0 or 4 kings
~5H–1 king
~5S–2 kings
~5NT–3 kings

Over time, bridge experts have modified these conventions in many ways. Partnerships should clarify their ace- and king-asking style before beginning play.