A turbocharger system comprises a first relatively small high-pressure (HP) turbocharger (1) and a second relatively large low pressure (LP) turbocharger (2). The turbine (6) of the LP turbocharger (2) is connected in series downstream of the turbine (4) of the HP turbocharger (1) in a first exhaust gas passage (11). An exhaust bypass flow passage (12) provides a bypass flow path around the HP turbine (4). A rotary valve (8) is located at a junction of the bypass flow passage (12) and a first exhaust gas flow passage (11). The rotary valve (8) comprises a valve rotor (19) which is rotatable to selectively permit or block flow to the LP turbine (6) from either the first exhaust gas passage (11) or the bypass gas passage (12). The rotary valve (8) is operated to at least partially restrict flow to the LP turbine to generate a braking back pressure.