Herts and Middlesex Wildlife Trust manages over 40 nature reserves covering nearly 810 hectares (2,000 acres) north of London, in Hertfordshire and the historic county of Middlesex, part of which is divided between the London boroughs of Barnet, Enfield, Harrow and Hillingdon.

The trust also encourages people to be active volunteers helping to maintain nature reserves.

By 1970 it had twenty reserves and in the same year it took over management of its first Site of Special Scientific Interest (SSSI), Blagrove Common.

[a] In 2007 it purchased Amwell Quarry, and started restoration which has now made the site internationally important for its wetland birds.

[5] The largest is King's Meads, at 96 hectares (240 acres); this is water meadows where 265 wildflower species have been recorded, and it is an important site for overwintering European stonechats.