The North Downs are a ridge of chalk hills and an area of downland in south-east England, that stretch from Farnham in Surrey to the White Cliffs of Dover in Kent. Much of the North Downs comprises two Areas of Outstanding Natural Beauty (AONBs): the Surrey Hills and the Kent Downs. The North Downs Way National Trail runs along the North Downs from Farnham to Dover.

The highest point in the North Downs is Botley Hill, Surrey (270 metres (890 ft) above sea level). The County Top of Kent is Betsom's Hill (251 m (823 ft) above sea level), which is less than 1 km from Westerham Heights, Bromley, the highest point in Greater London at an elevation of 245 m (804 ft).

This term is used to describe the characteristic landscape of 'elevated rolling grassy hills' in southern England, where chalk and limestone is exposed at the surface, acquiring this sense around the 14th century. The name "downs" is derived from the Celtic word "dun", meaning "fort" or "fastness" (and by extension "fortified settlement", from which it entered English as "town", similar to Germanic "burg"/"burough"), though the original meaning would have been "hill", as early forts were commonly hillforts - compare Germanic "burg" (fort) and "berg" (mountain). These hills are prefixed 'North' to distinguish them from a similar range of hills – the South Downs – which runs roughly parallel to them but some 50 km (31 mi) away on the southern edge of the Weald that divides the two ranges of hills.

The narrow spine of the Hog's Back between Farnham and Guildford forms the western extremity of the North Downs, whilst the cliffs between Folkestone and Deal terminate the ridge in the east. The North Downs cuesta has a steep south-facing scarp slope and a more gentle north-facing dip slope. Its southern boundary is defined by the low-lying Vale of Holmesdale at the foot of the escarpment, in which the underlying stratum is primarily gault clay. The northern boundary is less apparent but occurs where the chalk submerges below the more recent Paleocene deposits.

The Downs are highest near the Kent–Surrey border, often reaching heights in excess of 200 m (660 ft) above sea level at the crest of the escarpment. The highest point is Botley Hill in Surrey at 269 m (883 ft). The County top of Kent at Betsom's Hill, with a height of 251 m (823 ft), is nearby, and the highest point in Greater London, Westerham Heights, at 245 m (804 ft), is on the northern side of the same hill. East of the Medway Valley the Downs become broader and flatter, extending as far as the Isle of Thanet.

The ridge of the North Downs is intersected by the valleys of a series of rivers: the Wey, Mole, Darent, Medway and Stour. These drain much of the Weald to the south. The western rivers are tributaries of the Thames; they have carved steep valleys through the chalk and provide natural corridor routes. In addition to existing rivers, the Downs are crossed by a number of wind gaps – prehistoric river valleys no longer occupied by rivers – including those at Farnham, Betchworth, Caterham, Lyminge and Hawkinge. Except for the river valleys and wind gaps, the crest of the escarpment is almost continuous along its length. The dip slope is dissected by many small dry valleys, and in the broad eastern part in Kent, by further river valleys such as that of the Little Stour.

Leith Hill (the highest point in Surrey) is sometimes incorrectly referred to as part of the North Downs, but it is located on the parallel Greensand Ridge and does not consist of chalk.

The Downland of the North Downs consists of distinct lithostratigraphic units (the types of strata, the names of which are always capitalised):