Selby and Ainsty is a constituency^{[lower-alpha 1]} in North Yorkshire. It has been represented by Keir Mather from the Labour Party since 21 July 2023.

Further to the completion of the 2023 Periodic Review of Westminster constituencies, the seat will be subject to boundary changes which will involve the loss of the Ainsty area. As a consequence, it will revert to the name of Selby, to be first contested at the next general election.^[2]

For 2010, the Boundary Commission recommended the creation of this seat following a review of parliamentary representation in York and North Yorkshire. The constituency was formed from the former Selby constituency, except for some villages near York that were moved to the new York Outer constituency and rural areas south and east of Harrogate previously in the Vale of York constituency.

Until 2023, the seat had been won by the Conservative Party by a successively larger set of majorities each time it has been contested, though the 2017 general election had the unusual result of the Conservatives slightly increasing their majority despite a slight swing towards the Labour Party, mostly due to a significantly higher turnout.

On 12 June 2023 the seat became vacant following the formal resignation of the incumbent, Nigel Adams,^[3] and the resulting by-election returned Labour's Keir Mather.

The constituency consists of:

• The entire former District of Selby
• The electoral wards of Marston Moor, Ouseburn, Ribston, and Spofforth with Lower Wharfedale in the former Borough of Harrogate

The constituency is mainly rural. The only towns are Selby, Tadcaster, and Sherburn in Elmet. The rural areas include parts of the ancient Wapentake of the Ainsty of York.

In statistics

The constituency consists of Census Output Areas of two local government districts with similar characteristics: a working population whose income is close to the national average and lower than average reliance upon social housing.^[4] At the end of 2012, 2.2% of the population were claiming jobseekers’ allowance, compared with the regional average of 4.7%.^[5] The district contributing to the bulk of the seat has a low 14.5% of its population without a car, 21.2% of the population without qualifications, and a relatively high 26.1% with level 4 qualifications or above. 75.0% of homes were owned outright or on a mortgage by occupants as of the 2011 census across the Selby district.^[6]

• List of parliamentary constituencies in North Yorkshire