Neath (Welsh: Castell-nedd) is a constituency of the Senedd. It elects one Member of the Senedd by the first past the post method of election. Also, however, it is one of seven constituencies in the South Wales West electoral region, which elects four additional members, in addition to seven constituency members, to produce a degree of proportional representation for the region as a whole.

Since the creation of the assembly the constituency has returned a Labour AM, with varying majorities, from 7.7% to 26.8%. The current incumbent Jeremy Miles is one of the first openly gay elected Members of the Senedd.^[1] Plaid Cymru are Labour's main opposition in the seat.

In the election in 2016 the constituency got the highest vote share from an Independent in Steve Hunt with 8.1% of the vote. Hunt was the only independent to save his deposit.

The constituency was created for the first election to the Assembly, in 1999, with the name and boundaries of the Neath Westminster constituency. It is entirely within the preserved county of West Glamorgan.

The other six constituencies of the region are Aberavon, Bridgend, Gower, Ogmore, Swansea East and Swansea West.

In general elections for the Senedd, each voter has two votes. The first vote may be used to vote for a candidate to become the Member of the Senedd for the voter's constituency, elected by the first past the post system. The second vote may be used to vote for a regional closed party list of candidates. Additional member seats are allocated from the lists by the d'Hondt method, with constituency results being taken into account in the allocation.