Ash is a village and civil parish in the far west of the borough of Guildford, Surrey. Ash is on the eastern side of the River Blackwater, with a station on the Reading-Guildford-Gatwick line, and direct roads to Aldershot, Farnham and Guildford. The 2011 census counted the residents of the main ward of Ash, which excludes Ash Vale, as 6,120. Ash has a small museum in the local cemetery chapel, a large secondary school and a library.

The southern part of the parish, including St. Peter's Church and Ash village, is on the London Clay; but the greater portion, once including Frimley, covers the western side of the ridge of Bagshot Sands, which is divided from Chobham Ridges by the dip through which the Basingstoke Canal and railway run, and is known as Ash Common, Fox Hills and Claygate Common (now in Surrey Wildlife Trust and MoD use).

Ash Green is the community closer to the Hog's Back, along which the east–west A31 runs, and has Whitegate Copse and arable fields as a green buffer on all sides.

The hamlet used to be served by Ash Green Halt. The railway station had two platforms and was situated on the Tongham branch of the Alton line before passenger services were withdrawn in 1937 along with Tongham station and ultimately the branch closed in 1960. Though the tracks have been long removed, the stretch of land from Tongham through Christmas Pie, where the route of the branch line still exists, is a popular attraction for cyclists and walkers. Ash Green Halt's station building, complete with its Southern Railway-style sign, still stands and has been converted into a house.

From the prehistoric period, a few neolithic implements have been found and these are now in the Surrey Archaeological Society's Museum at Guildford.

There is no mention of a mill under Henley in the Domesday Book, but it is certain that a mill existed at Ash from comparatively early times, for in 1322 the Abbot of Chertsey ordered a new windmill to be built at Ash. Windmills were comparatively new in England then, and it may have been in place of a small water-mill of earlier date. There seems to be no later record of it.

The two manors existed. Ash (Esche, 7th century; Asshe, Assche, 14th century) shares with the other a prominent social history starting with at least the Norman period of the Domesday Book whose commissioners wrote "Azor granted [part of Henley known as Ash] for his soul to Chertsey in the time of King William. Later a 1279 chartulary of Chertsey Abbey records the prohibition of any perpetual title of institutions (as the Abbey states, vulgarly called the prohibition of mortmain) as led here to 11 acres in Ash with sufficient common pasture for his flocks and herds being held by Robert de Zathe, while Geoffrey de Bacsete (Bagshot) and his brother William had 28 acres. The Atwaters of West Clandon also held land in Ash. Nonetheless, from the church's freehold, overall control passed from 1537 in the Dissolution of the Monasteries to Winchester College. Henley, also seen as Henle, (14th century) and Suth henle and Henle on the Heth usually to distinguish Henley on Thames has hosted a long list of prominent figures. The de Henley, de Molyns , the crown as owner from Edward I to Charles I, Arthur Squib whose daughter married its next owner John Glynne, occupied briefly by the Duke of Roxburgh then via Glynne's granddaughter's husband, Sir Richard Child, created Earl of Tylney it then passed to ambassador and diplomat Solomon Dayrolles, upon whose death John Halsey bought it, whose family owned it from the 18th to 20th centuries.

The church is dedicated to St Peter, which distinguishes it from the other English places named Ash; Ash, in Kent, near Dartford, has a church to St Peter and St Paul.