Aspects of the present invention relate to an active diffuser mechanism for a vehicle comprising a mounting mechanism for connecting a diffuser body to a body of a vehicle such that the diffuser body is moveable between a stowed position and a deployed position in which an airflow surface of the diffuser body is spaced further away from the body of the vehicle than in the stowed position. The mounting mechanism comprises a linkage mechanism configured such that the diffuser body follows a linear translation path and a rotational path during movement from the stowed position to the deployed position. Aspects of the present invention also related to an active diffuser assembly, an active diffuser system and a vehicle comprising such an active diffuser mechanism.