2021 Chesham and Amersham by-election

A by-election for the United Kingdom parliamentary constituency of Chesham and Amersham was held on 17 June 2021, following the death of incumbent Conservative Party MP Dame Cheryl Gillan. The Liberal Democrat candidate, Sarah Green, won the by-election with a swing from the Conservatives of 25.2%. This was the first time a non-Conservative candidate had won this seat since its formation in 1974.

This was the first of four by-elections the Liberal Democrats gained from the Conservatives in this parliament; they subsequently won the by-elections in North Shropshire, in December 2021, in Tiverton and Honiton, in June 2022, and in Somerton and Frome, in July 2023.