A variable geometry turbine comprising: a turbine wheel supported in a housing for rotation about a turbine axis; an annular primary inlet passageway extending radially inwards towards the turbine wheel, the primary inlet passageway being defined between a surface of a radial wall of a moveable wall member and a surface of a facing wall of the housing; the moveable wall member being mounted within an annular cavity provided within the housing, the movable wall member being moveable axially to vary the width of the primary inlet passageway; an annular seal being mounted to one of the movable wall member and an adjacent housing member to provide a seal between adjacent surfaces of the movable wall member and the housing member respectively; characterised in that a bypass passage is provided in the other of said movable wall member and housing member, the bypass passage extending from an inlet bypass port to an outlet bypass port, said inlet and outlet bypass ports being axially spaced from each other and provided in said adjacent surface of said other of the movable wall member and housing member; a secondary inlet passageway fluidly connecting a region of the cavity outboard of the seal to the turbine wheel such that flow in the secondary inlet passageway bypasses at least a portion of the primary inlet passageway; the bypass passage and the annular seal being arranged such that as the movable wall member moves axially, the annular seal moves axially relative to the inlet and outlet bypass ports so as to vary the extent of flow that may pass from a region of the cavity inboard of the seal, through the bypass passage to the secondary inlet passageway. a turbine wheel supported in a housing for rotation about a turbine axis; an annular primary inlet passageway extending radially inwards towards the turbine wheel, the primary inlet passageway being defined between a surface of a radial wall of a moveable wall member and a surface of a facing wall of the housing; the moveable wall member being mounted within an annular cavity provided within the housing, the movable wall member being moveable axially to vary the width of the primary inlet passageway; an annular seal being mounted to one of the movable wall member and an adjacent housing member to provide a seal between adjacent surfaces of the movable wall member and the housing member respectively; characterised in that a bypass passage is provided in the other of said movable wall member and housing member, the bypass passage extending from an inlet bypass port to an outlet bypass port, said inlet and outlet bypass ports being axially spaced from each other and provided in said adjacent surface of said other of the movable wall member and housing member; a secondary inlet passageway fluidly connecting a region of the cavity outboard of the seal to the turbine wheel such that flow in the secondary inlet passageway bypasses at least a portion of the primary inlet passageway; the bypass passage and the annular seal being arranged such that as the movable wall member moves axially, the annular seal moves axially relative to the inlet and outlet bypass ports so as to vary the extent of flow that may pass from a region of the cavity inboard of the seal, through the bypass passage to the secondary inlet passageway.