Harbour Antibodies BV was established in 2006 to use transgenic mouse technology developed in the laboratory of Professor Frank Grosveld at Erasmus MC (Rotterdam, the Netherlands) for engineering mice to produce high affinity human antibodies. The company has developed two types of human immunoglobulin gene transgenic mice: mice that generate “conventional” tetrameric antibodies comprising two heavy and two light immunoglobulin chains (H2L2); and alternatively, mice that generate heavy chain only antibodies comprising two immunoglobulin heavy chains with no light chains (HCAbs). Availability of HCAbs facilitates the generation of soluble human VH domains (human heavy chain variable region domains), the minimal immunoglobulin recognition unit, and thus the construction of novel multi-functional molecules comprising either two (or more) VH domains or one VH domain coupled to other molecules. Both Harbour transgenic mouse lines are now available to licensing partners.