[2][3] It is similar to Blackwood but uses 4♣ instead of 4NT as a relay (asking) bid to inquire about the number of aces held by partner.
Gerber is used primarily after notrump openings, responses, and rebids, making it a complement to Blackwood rather than a replacement.
Because bidding and making a slam or grand slam contract in bridge gains significant bonus scoring points, partnerships will strive to bid them whenever their combined card assets are deemed sufficient.
Knowing the number of aces and kings jointly held is usually crucial to this decision and Gerber is one of several bridge conventions used to ascertain the necessary information.
The criteria for its application vary amongst users and alternatives are detailed below; likewise, a number of response schemes have been developed over the years.