Horsham (/ˈhɔːrʃəm/) is a constituency^{[n 1]} represented in the House of Commons of the UK Parliament,^{[n 2]} centred on the eponymous town in West Sussex, its former rural district and part of another rural district. Its Member of Parliament (MP) was Francis Maude between 1997 and 2015; since then it has been Jeremy Quin, both of the Conservative Party.

1885–1918: The Sessional Divisions of Horsham, Midhurst, Petworth, the civil parish of Crawley.

1945–1950: The Urban Districts of Horsham, Shoreham-by-Sea, Southwick, the Rural Districts of Chanctonbury and Horsham.

1950–1974: The Urban District of Horsham, the Rural Districts of Horsham, Midhurst, Petworth.

1983–1997: The District of Horsham.

1997–2010: The District of Horsham wards of Billingshurst, Broadbridge Heath, Cowfold, Denne, Forest, Holbrook, Itchingfield and Shipley, Nuthurst, Riverside, Roffey North, Rudgwick, Rusper, Slinfold, Southwater, Trafalgar, Warnham, the District of Mid Sussex wards of Balcombe, Copthorne and Worth, Crawley Down, Slaugham, Turners Hill, the District of Chichester wards of Plaistow and Wisborough Green.

2010–present: The District of Horsham wards of Billingshurst and Shipley, Broadbridge Heath, Denne, Forest, Holbrook East, Holbrook West, Horsham Park, Itchingfield, Slinfold and Warnham, Nuthurst, Roffey North, Roffey South, Rudgwick, Rusper and Colgate, Southwater, and Trafalgar, and the District of Mid Sussex wards of Ardingly and Balcombe, Copthorne and Worth, and Crawley Down and Turners Hill.

The constituency is located in a northern part of West Sussex, bordering the constituencies of Arundel and South Downs, Mid Sussex. It is centred slightly east of the town of Horsham and is rectangular with the exception of a noticeable gap formed by the smaller constituency of Crawley.

Horsham has existed as a constituency for three distinct periods. It first sent members to Parliament in 1295. However, the constituency was abolished in 1918 to make way for Horsham and Worthing. In 1945 the constituency was recreated, until 1974 when Horsham and Crawley was created. In 1983 the constituency of Horsham was again created and has existed since.

The constituency (including its brief larger versions under other names) has been represented by members of the Conservative Party since 1880, making it the longest held Conservative seat and not normally with marginal majorities making it a safe seat, though just outside the top twenty Conservative seats sorted by majority.^[3]

• List of parliamentary constituencies in West Sussex
• Horsham