A variable geometry turbine comprises a turbine wheel supported in a housing for rotation about a turbine axis. The housing defines an annular inlet passage around an inducer portion of the turbine wheel and an outlet passage including a tubular wall disposed around an exducer portion of the turbine wheel; the inlet passage is defined between first and second radial inlet surfaces, one of the inlet surfaces being defined by a moveable wall member and the other of the inlet surfaces being defined by a facing wall of said housing. The moveable wall member is moveable relative to the facing wall of the housing along the turbine axis to vary the size of the inlet passageway. The moveable wall member is displaceably mounted within an annular cavity defined between the tubular wall and a surrounding wall of the housing.