Avonmouth (/ˈeɪ.vənmaʊθ/ AY-vən-mowth) is a port and outer suburb of Bristol, England, on the north bank of the mouth of the River Avon and the eastern shore of the Severn Estuary. Part of the Port of Bristol, Avonmouth Docks is important to the region's maritime economy, hosting large vessels for the unloading and exporting of heavier goods. Much of the land use is industrial, including warehousing, light industry, electrical power and sanitation. The M5 motorway bisects the neighbourhood, with junctions onto the A4 road and M49 motorway, and it has stations on the Severn Beach Line railway.

Avonmouth is part of the Bristol City Council electoral ward of Avonmouth and Lawrence Weston, which also includes Shirehampton and the western end of Lawrence Weston.

Avonmouth is approximately rectangular, its length favouring the Severn shore, and sits on the north bank of the Avon, west-north-west of Bristol city centre. Both estuaries have been defensively embanked, primarily to allow the construction of the large Avonmouth Docks, which occupy most of the western part. The related Royal Portbury Dock is across the Avon (in Easton-in-Gordano). Avonmouth is home to chemical manufacturing plants, and north of the Avonmouth Docks is the gas-fired Seabank Power Station. Its light industrial and warehouse companies include Nisbets.

Avonmouth is the only part of Bristol west of the M5 motorway. The long-established residential area is between the industrialised zone and the motorway. The Avonmouth Bridge takes the motorway over the Avon to Somerset. The M49 motorway runs from the M5 at Avonmouth north to the M4 motorway at the Second Severn Crossing to Wales. The old Severn Bridge and the M48 motorway are linked to Avonmouth by the A403. The Welsh cities of Newport and Cardiff are visible from Avonmouth's coastline.

The Portway, part of the A4, connects Avonmouth with the centre of Bristol. Avonmouth is also served by a usually hourly train service on the Severn Beach Line to central Bristol from Avonmouth railway station, Portway Park & Ride (in the southeast of the neighbourhood) and St Andrews Road (in the western industrial zone).

A new deep-sea container terminal has been proposed for Avonmouth.

Avonmouth or the mouth of the River Avon was recorded as Afenemuþan in the Anglo-Saxon Chronicle under the years 915 or 918 and 1052, but it is clear from the context that the name does not refer to a settlement. References to "Afenemuþan" in the chronicles describe how Edward the Elder stationed his men there as well as at "Sæfernmuþan" (the mouth of the River Severn). The Vikings reached Anglo‑Saxon shores by sea and could travel far inland because their ships had hulls that sat high in water and required little depth to float (i.e. had a shallow draught), the Avon and Severn were rivers and thus vulnerable to Viking penetration.

In Old English therefore Afenemuþan was a compound noun made up of the word "Avon" - derived from the Common Brittonic abona, "river", which survives in the Welsh word afon [ˈavɔn], and the word muþan the dative form of muþa meaning mouth.