The Mens is a 205.2-hectare (507-acre) biological Site of Special Scientific Interest west of Billingshurst in West Sussex. It is a Nature Conservation Review site, Grade I and a Special Area of Conservation. An area of 166 hectares (410 acres) south of the A272 road is managed as a nature reserve by the Sussex Wildlife Trust.

This large area of woodland has diverse breeding birds and rich lichen and fungal floras. There are many rare beetles and a fly which is endangered with extinction, Chelostoma curvinervis. All three British species of woodpecker breed on the site, together with other woodland species such as nightingales, woodcocks and wood warblers.