"Si Tú Supieras" (English: "If You Knew") is a song written by Kike Santander and performed by Mexican recording artist Alejandro Fernández. It was co-produced by Santander and Emilio Estefan and was released as the first single from Me Estoy Enamorando by Sony Music Mexico on August 1997. The song is a bolero-pop ballad with ranchera influences and portrays the singer yearning for his lover to know how much she means to him. A music video was made for the track and was used as the main theme for the Mexican telenovela María Isabel.
It reached the top of the Billboard Hot Latin Songs chart in the United States and spent a total of six weeks at this position. The recording led to Fernández winning the Lo Nuestro Award for Pop Song of the Year and the Eres awards for Best Song and Best Musical Theme in 1998 while Santander received the BMI Latin Award for Song of the Year in 1999. "Si Tú Supieras" has been covered by other artists including Tony Vega, Manuel Mijares, Noel Schajris, and Chamin Correa. Vega's version peaked at number five on the Hot Latin Songs chart in the US.