Muiderberg is a bidding convention in the card game bridge. It is a two-level preemptive opening based on a two-suiter with precisely a five-card major and a minor suit (four-card or longer). In Muiderberg the 2 opening denotes five hearts and an unknown minor suit, whilst 2 denotes five spades and an unknown minor suit. The convention is also known as the Dutch Two, Lucas Two or Woo Two (mainly UK) opening. The convention is named after the Dutch village Muiderberg, the residence of the designers of the convention – Onno Janssens and Willem Boegem. Responses The partner of the Muiderberg opener can take the following actions: pass (with tolerance for the opened suit) bid 3 (a pass-or-correct bid) bid 3 to invite for game in the major suit bid 2 (over 2) as a contract improvement (opener is allowed to raise with a suitable hand) bid 3/ (opener's suit) as a preemptive raise bid 3/ (other major) which is non-forcing but invitational ask for the minor suit using a 2NT relay bid with a strong hand. The 2NT response is often defined as forcing to game, for example in Biedermeijer and AcolPlus. In particular, with a strong hand with a good suit of its own or with support for partner's opened suit, responder must bid 2NT first, as there is no other way to establish a force. The Muiderberg opener can respond in several ways to the 2NT answer: bid 3 with a minimum and clubs / with four clubs bid 3 with a minimum and diamonds / with four diamonds bid 3 with a maximum and clubs / with five or more clubs bid 3 with a maximum and diamonds / with five or more diamonds bid 3NT with 4-4 in both minors bid 4/ with a 6+ cards in the bid suit Both approaches (2NT forcing to game or forcing for one round only) are equally popular. In competition, 3 is natural (opener is expected to pass) while 2NT asks for opener's minor suit and is not necessarily strong. Further, 4/ are defined as fit-bids in competition. Variants Partnerships may choose to play Muiderberg Twos (or the variants below) as: (a) at least 5-4 shape, (b) at least 5-5 shape, or (c) at least 5-4 when non-vulnerable but at least 5-5 when vulnerable, for added safety. Statistically, 5-4 hands are about four times as common as 5-5.