Coulsdon Common lies between Old Coulsdon and Caterham on the Hill, on the southern edge of Greater London. It covers an area of 51 hectares (127 acres) and it is owned and managed by the Corporation of London under the Corporation of London (Open Spaces) Act of 1878.

Nearly half of Coulsdon Common is now covered by woodland but most of this has developed since the latter part of the 19th century. Prior to this the land was probably heathland and, due to the poor soil, used only for grazing. Without the many trees that now occupy much of the area, it would have been very windswept and therefore an excellent position for the two windmills, which used to exist within its boundaries. Gorse and heather can still be found today in some of the small glades that exist.

The dominant tree is pedunculate oak but other frequently found species include ash, birch and cherry. The understory is largely made up from hawthorn, holly, yew and elder whilst the undergrowth is mainly brambles, bracken, and woodland grasses.

There are some areas of 'ancient' woodland, which have been established for hundreds of years, these include Rydons Wood and the section of woodland next to Hayes Lane within the areas known as Merlewood Near and Merlewood Far, the ground flora here is much richer, including bluebells, wood anenomes and dog's mercury.

There is a pond within Stites Hill Wood, where large numbers of frogs, newts and dragonflies breed.

The grassland that remains includes chalk, neutral and acid grassland and this is managed by a combination of grazing, haymaking and mowing. The chalk grassland can be found in the north east and supports a wide variety of flora, including greater yellow rattle, yellow rattle, cowslip and salad burnet. Species to be found in the neutral grassland in the Rydon's Wood area include bird's foot trefoil, and knapweed. The acid grassland around the football pitch area has tormentil and sheep sorrel.