Alnham (/ˈælnəm/, /ˈjɛldəm/) is a hamlet and civil parish in Northumberland, England. It is about 14 miles (23 km) west of Alnwick, and is about 6 miles (10 km) from the Scottish border, on the south of a small tributary of the River Aln. The village stands on uneven ground, sloping from south to north, at the foot of the southern outliers of the Cheviot Hills. The River Aln flows eastward through the village from its source in the Cheviot Hills down to the coast. The layout of the village appears to have been dictated by the river. The estimated population taken at the 2011 Census was around 245.

There is evidence of human occupation in Alnham and the surrounding areas dating from prehistoric times. The remains of a medieval settlement, hillforts, and other historic buildings can still be found in the village today. Due to its location, Alnham often suffered in the Anglo-Scottish border conflict during its history. The economy of Alnham has been focused on agriculture throughout its existence as a settlement.

The name "Alnham" derives from the Old English hām (homestead) and the Celtic river-name Aln or Alaunos, meaning "homestead on the River Aln". Variations of the name have been recorded over time, including: Alneham (1331), Elnam (1509), Ayneham (1557), and Ailnham (1663). Alnham has also historically been called "Yeldom", and in the Magna Brittannia of 1724 it is mentioned as being usually called "Yarwell".

There is no direct evidence of Paleolithic or Mesolithic human occupation within Alnham, although it is possible that the Cheviot slopes to the west of Alnham provided a wooded area perfect for seasonal foraging parties. The only evidence of Neolithic habitation is a cup-marked stone found at Alnham Northfield. Bronze Age occupation of Alnham is more evident. A rare bronze spearhead has been found at High Bleakhope to the north-west of Alnham, possibly indicating occupation by an elite social class. The remote and elevated location of High Bleakhope suggests that the spearhead was placed there as an offering to a deity. A number of cairns have been discovered in the surrounding area which may have been constructed in the Bronze Age. Unenclosed settlements, common in the Cheviots through the Iron Age and Bronze Age, have also been found in the surrounding area. Two Iron Age palisaded enclosures have been discovered on High Knowes to the north-west of Alnham. Castle Hill in Alnham is an example of a Cheviot multivallate hillfort and is likely to have existed by the Iron Age. Remains of hut circles within the inner closure suggest that Castle Hill was a settlement with a small population. Evidence of the Romans in the Cheviots, which is situated beyond the Roman frontier, is difficult to detect and distinguish from the Iron Age due to their limited cultural influence. The closest settlement to Alnham which is considered to be Roman can be found on Castle Hill.

During the Middle Ages Alnham was an important location, as indicated by its ancient buildings, castle mound, and pele tower. There is evidence that it was a populous village and reached its peak of prosperity in the late 13th century. The Church of St Michaels was first recorded in an 1184 charter in which William de Vesci granted Alnham and its tithes to Alnwick Abbey. During the reigns of Henry III and Edward I, Alnham was part of the lordship and estate of William de Vesci (in 1242) and John de Vesci (in 1289). In 1293 William de Vesci claimed free Chase in Alnham, but with no male heirs, his property was passed to Antony Bek (Bishop of Durham) after his death. Bishop Bek sold the Barony of Alnwick, which included Alnham, to Henry de Percy, 1st Baron Percy. From that point onwards, Alnham remained in the same descent as the rest of the Percy estates.

The history of Alnham was often troubled, including by climatic deterioration and harvest failure in the early 14th century, and the Black Death. These events caused the population to reduce significantly. In 1352, after the Black Death, there were 34 holdings, half of which were unoccupied. The surviving residents of Alnham, however, may have benefitted somewhat from this reduction in population and secured better rights: the Inquisition for Henry de Percy in 1368 reveals that the bondages and cottages were held by "tenants-at-will", in comparison to earlier non-contractual tenancies which owed labour services to a lord. Being situated in a precarious position between the English and Scottish borders, Anglo-Scottish combat also caused disruption in Alnham. Alnham suffered at the hand of Scottish raids during the reign of Henry VIII. Two letters from the Earl of Northumberland to the King, dating from October and November 1532, describe how the Scots came across the borders and rampaged Alnham and surrounding towns. The tower at Alnham appears to have suffered damage from the Scottish raids as it was reported to have been in a bad condition by 1541. The dangerous position of Alnham between the English and Scottish borders is again revealed in a survey of the manor from 1615, which reads:

the toune and manor of Alneham is parcell of the Barony of Alnewicke. The soyle thereof is good and fertile but the tenants have been greatly impoverished and disabled by the Scots and often English thieves by reason that the said toune lieth open to the great wastes between the two realmes.

Alnham was a significant agricultural centre in the early 17th century. Robert Norton's map of the Duke of Northumberland's Alnham Estate from 1619 reveals Alnham's meadowland consisted of four large common fields, 70 acres of arable land, and 168 acres of "Alnham oxe pasture". From the 18th century onwards, Alnham underwent a period of decay and transformation. In 1724, the Magna Brittannia described Alnham as being "pretty large". However, an undated map from pre-1750 shows a dwindling number of cottages, Seymour's Survey of c. 1756 records five cottages, and in the Enclosure Award of 1776 the village is recorded as having only two farms and three cottages. This decay can be attributed to the 17th and 18th century policy of leasing tenement lands to a single tenant, resulting in the amalgamation of land formerly owned by tenants-at-will into larger farmholdings. Transformation came about later in the 18th century: Alnham Common was first recorded in a survey of 1702 and was divided and apportioned in 1776. The grounds were divided up into holdings along the east and southeast sides of the township and a new road was built through the village. The Duke of Northumberland secured the largest share of the land: 1,379 acres of infield ground and 6590 acres of common. Further divisions of the land were granted to Alexander Collingwood, Charles Byrne, Percival Clennel, and the Vicar of Alnham.

In the 19th century, the village of Alnham consisted of three farms, a church, a vicarage, a Church of England school (constructed in 1870), and six cottages. Farming continued to be the focus of economic activity. By the late 19th century, Alnham Parish covered around 12,000 acres with the township of Alnham being by far the largest at 9535 acres. The population of Alnham in 1801 was 233 and remained relatively stable throughout the century, dropping to 205 by 1891. The 1831 census revealed that the majority of male residents aged over 20 in Alnham Parish was labourers or servants (45 men). A smaller proportion were employers and professionals (8 men), or "middling sorts" (15 men), which included small farmers and skilled workers.

The village did not develop much during the 20th century. The only new building to be constructed in this period was the War Memorial Hall erected in 1921. The population gradually declined owing to mechanisation and reduction in farming incomes.

Alnham falls within the North Core Strategy Delivery Area of Northumberland – one of the least populated areas of England with 26 residents per square km, compared to the county average of 63. In 2001, the parish of Whittingham and Alnham had a total usual population of 505. In 2011, Alnham Parish had an estimated population of 245. 20.4% of residents were aged 0-15 and 10.2% of residents were aged 65+. 100% of residents identified as white. The majority of residents (68.6%) were Christian with the remaining population either having an 'other' religion, no religion, or did not state religion. 81.3% of residents aged 16-74 were economically active with agriculture, forestry and fishing being the most common industry (25.7%).

Throughout its history, Alnham has been incorporated in various territorial units. In the Medieval period, Alnham formed one of the manors of the Barony of Alnwick held by the Vesci lineage beginning in the early 12th century and ending in 1310. The Barony was then sold to Henry de Percy and remains in the hands of the Percy family today. The Parish of Alnham in the 19th century contained the townships of Alnham, Prendwick, Scrainwood and Unthank. These townships were recorded as separate localities in the feudal aid of 1242.

In the UK Parliament, Alnham is part of the Berwick-upon-Tweed Parliament constituency which has been represented by Anne-Marie Trevelyan (Conservative) since May 2015. Prior to May 2015, the seat was represented by Alan Beith (Liberal Democrats). In local government, Alnham is part of the Rothbury Ward and is represented by Steven Christopher Bridgett (Independent). At the Parish council level, Alnham is part of Whittingham Parish Council which comprises the former three separate parishes of Alnham, Callaly and Whittingham.

There are seven listed structures in Alnham, including old buildings, the Church, and a Medieval settlement.