Louth and Horncastle is a constituency^{[n 1]} in Lincolnshire represented in the House of Commons of the UK Parliament since 2015 by Victoria Atkins, a Conservative.^{[n 2]}

1997–2010: The District of East Lindsey wards of Alford, Chapel St Leonards, Coningsby, Donington on Bain, Fotherby, Grimoldby, Halton Holegate, Hogsthorpe, Holton le Clay, Horncastle, Hundleby, Legbourne, Mablethorpe, Mareham le Fen, Marshchapel, New Leake, North Holme, North Somercotes, North Thoresby, Partney, Priory, Roughton, St James', St Margaret's, St Mary's, St Michael's, Spilsby, Sutton and Trusthorpe, Tattershall, Tetford, Tetney, Theddlethorpe St Helen, Trinity, Willoughby with Sloothby, Withern with Stain, and Woodhall Spa.

2010–present: The District of East Lindsey wards of Alford, Binbrook, Chapel St Leonards, Coningsby and Tattershall, Grimoldby, Halton Holegate, Holton le Clay, Horncastle, Hundleby, Legbourne, Ludford, Mablethorpe Central, Mablethorpe East, Mablethorpe North, Mareham le Fen, Marshchapel, North Holme, North Somercotes, North Thoresby, Priory, Roughton, St James', St Margaret's, St Mary's, St Michael's, Skidbrooke with Saltfleet Haven, Spilsby, Sutton on Sea North, Sutton on Sea South, Tetford, Tetney, Trinity, Trusthorpe and Mablethorpe South, Willoughby with Sloothby, Withern with Stain, and Woodhall Spa.

This large stretch of Lincolnshire coastline includes the seaside resorts of Mablethorpe and Sutton-on-Sea, this immediate coastline has a minority of small output areas with severe deprivation following the decline of the tourism industry apart from holiday cottages, being further north than popular family resorts in Skegness.^[2] The seat's eponymous towns of Louth and Horncastle lie inland amid a rural area of the Lincolnshire Wolds where farming is an important sector, with most constituents on modest to mid-level income and low unemployment. ^{[citation needed]}

The seat was created in 1997. Conservatives have been dominant in the area for decades, the closest result was in 1997, when a Labour Party candidate came the closest of any opponents to being elected.

The MP for this seat is Victoria Atkins. She succeeded Peter Tapsell at the 2015 general election. He previously represented the predecessor seats of East Lindsey and Horncastle from 1966 to 1997, and before that represented Nottingham West from 1959 to 1964 before being defeated by Labour. Prior to standing down, he was the longest-serving Conservative MP, albeit with the break in service, and from 2001, he was the only MP of any party first elected in the 1950s. Following the retirement of Alan Williams, Tapsell became, on his re-election in 2010, Father of the House. He was succeeded in the honorific position in 2015 by Sir Gerald Kaufman.

Before 1997, see East Lindsey

• Louth constituency (1885–1983)
• List of parliamentary constituencies in Lincolnshire