An overhead-camshaft internal combustion engine is disclosed, in which the fuel pumps are arranged to use efficiently the space within a cylinder head assembly of the engine. The cylinder head assembly includes a cylinder head block, and the engine comprises a camshaft rotatable about a camshaft axis and having a plurality of inlet and exhaust cams for actuating associated inlet and exhaust valves of the engine, and at least one fuel pump comprising a unit pump assembly driven directly by a respective pump cam provided on the camshaft. The engine further comprises a plurality of rocker arms driven by the inlet and exhaust cams and arranged to actuate the inlet and exhaust valves. Each rocker arm is pivotable about a rocker arm axis which is substantially parallel to the camshaft axis. The or each pump assembly is mounted between the rocker arm axis and the cylinder head block.