Thatcham is an historic market town in the county of Berkshire, England, centred 3 miles (5 km) east of Newbury, 14 miles (24 km) west of Reading and 54 miles (87 km) west of London. Its population grew rapidly in the second half of the 20th century: from 5,000 in 1951 and 7,500 in 1961 to 22,824 in 2001. During World War II, Thatcham housed one of the biggest Prisoner of War camps in the South, known as camp 1001.

Thatcham straddles the River Kennet, the Kennet and Avon Canal, the A4. It is served by Thatcham railway station on the line between Reading and Newbury. Local employment is chiefly in light industrial premises, sales and distribution, retail and public sectors; see also West Berkshire, its district. Although there are many primary schools in the area, the only secondary school in Thatcham is the Kennet School.

The area has evidence of occupation dating from prehistoric times and was listed in the Guinness Book of Records as the strongest claimant to being the oldest continuously inhabited place in Britain[citation needed]. The well-preserved remains of a Mesolithic settlements dubiously dating from 8400 to 7700 BC have been found in its vicinity. Evidence also exists of Bronze and Iron Age settlements and of Romano-British activity.

The name may have been derived from that of a Saxon chief called Tace (or perhaps Tac or Tec), who established a village in around AD 500. The settlement might have been known as Taceham - ham meaning hamlet in Saxon. However one of the earliest written references in c.951 and c.975 records it as Thaecham. The Thaec comes from the Saxon þæc or thaec meaning roof-covering. By the time of Domesday Norman Conquest in 1086 the name had altered slightly to Taceham before going through several minor changes until the current form was adopted in the 16th century.

The town had a period of great prosperity around 1304 when the Chapel of St. Thomas the Martyr on the A4, now called the Old Bluecoat School, was granted permission to hold services. At that time the population was larger than Newbury's. There is a Norman parish church of St. Mary, which was largely reconstructed in 1857. This is believed to be built on the same site as an earlier Saxon church. It was also previously known as St. Luke's.

In 1121 King Henry I founded the great Abbey of Reading and endowed it with many gifts of land, including the Manor of Thatcham. At the same time Thatcham Hundred ceased to exist: the western part was transferred to Faircross Hundred, and the remainder to the Hundred of Reading.

In 1141 Thatcham Church, previously the property of the Diocese of Salisbury, was granted to Reading Abbey by the Empress Matilda, who at the same time confirmed her father's gift of the manor to the Abbey.

Thatcham has a site of Special Scientific Interest (SSSI) just to the south of the town, called Thatcham Reed Beds - a 67.4-hectare (167-acre) biological Site of Special Scientific Interest. Thatcham's network of gravel pits, reedbed, woodland, hedges, and grassland is rich in wildlife and has been made into The Nature Discovery Centre by the Royal Society for the Protection of Birds.