Rayo Vallecano de Madrid, S.A.D. ([ˈraʝo βaʎeˈkano ðe maˈðɾið]), often abbreviated to Rayo (Spanish for "thunderbolt"), is a Spanish professional football club based in Madrid, in the neighbourhood of Vallecas. Rayo was founded on 29 May 1924, and currently compete in La Liga following promotion from the 2020–21 Segunda División. Home games are held at the 14,708-seater Campo de Fútbol de Vallecas stadium.

Rayo has competed in one European competition, the UEFA Cup in the 2000–01 season. The club made it to the quarter-finals before losing to fellow Spanish club Alavés 4–2 on aggregate.

By historical standard, Rayo is the third best club in Community of Madrid, after Real Madrid and Atlético Madrid.

Rayo Vallecano was founded on 29 May 1924 in the hometown of Prudencia Priego, wife of the club's first president Julián Huerta. Greatly inspired by River Plate (a Football club from Argentina), in 1949, after an agreement with Atlético Madrid, a red diagonal stripe was added to the team's kit, and the club reached Tercera División for the first time in its history.

One of the perennial yo-yo clubs of Spanish football, and always in the shadow of the two biggest clubs in the city (Real Madrid and Atlético Madrid), Rayo Vallecano spent many years during the 1980s and 1990s moving back and forth between La Liga and Segunda División. The 1983-84 season was the worst during the 1980s. The club finished in the last position in Segunda División and was relegated to Segunda División B.