A method of attaching a tip extension to a wind turbine blade is described. The method comprises: fitting the tip extension over a tip end of the blade such that an overlap region is defined between an outer surface of the blade and an inner surface of the tip extension; and supplying adhesive to the overlap region via one or more holes provided in the tip extension to bond the tip extension to the blade. In preferred embodiments, adhesive dams are provided in the overlap region to define bond cavities and constrain the adhesive within the bond cavities. An assembly comprising a wind turbine blade and a tip extension bonded thereto is also described.