An apparatus for positioning sheets of material in a wind turbine blade mold to form a shell of a wind turbine blade, the mold having a mold surface defining the profile of a portion of the shell, the apparatus comprising: a rail that, in use, is mounted proximate to the mold and follows a path in a direction along the longitudinal length of the mold; and a sheet mounting apparatus coupled to the rail, the mounting apparatus configured to releasably hold a sheet of material and to move along the rail.