Abstract: A window assembly (30) comprising a frame (36) in which are received sliding and security members. The security member has ventilating and non-ventilating parts (40, 32), with the sliding member (34) being slidably moveable over the security member between a first position in which air may pass through the ventilating part (40) so as to ventilate the room in which the window assembly (30) is located, and a second position in which no such ventilation can occur. The ventilating part 40 may comprise a grille, perforated sheet, lattice arrangement or the like.