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).
[2] The partner of the Muiderberg opener can take the following actions: The 2NT response is often defined as forcing to game, for example in Biedermeijer and AcolPlus.
Particularly in the UK, the term Lucas Two is often used to describe what is actually a Muiderberg Two, where the second suit has to be a minor; this makes it safer for responder to explore for a second-suit fit if short in opener's longest suit.
A difficulty with Muiderberg and Lucas Twos is that it is no longer possible to make a Weak Two bid with a single-suited major.