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.[1]
The convention is named after the Dutch village Muiderberg, the residence of the designers of the convention – Onno Janssens and Willem Boegem.[2]