Abstract: A window stop is provided. The window stop includes a housing defining a cavity and having mount structure. The mount structure is adapted to be mounted to a wall having a thickness between a range of thicknesses from a minimum to a maximum thickness. A bolt is mounted within the cavity and moveable between a retracted position wherein the bolt is substantially located within the housing and a locking position wherein the bolt extends from within the cavity. Also provided is means for releasably holding the bolt in the retracted position and biasing means between the housing and the bolt for biasing the bolt towards the extended position.