Polycrystalline magnesium of 99.8 wt.% purity was subjected to high-pressure torsion (HPT) at room temperature. A special technique was developed in order to enable HPT of Mg up to very high shear strains of 115 and hydrostatic pressures of 4 GPa. The texture development during HPT was investigated by systematic X-ray texture measurements. It can be described by a stationary oblique B fibre characteristic of hexagonal metals subjected to simple shear. From the measured shear strain and pressure dependences of the B fibre and from microstructure investigations by TEM, it is concluded that also mechanisms of both dynamic and of static recrystallization contribute to the texture evolution.