"This I Promise You" is a ballad by the American boy band NSYNC. It was released in November 2000 as the third and final single in the United States and the fourth and final single in Europe from their second studio album, No Strings Attached, in 2000. The song is included on all three of the band's compilation albums: Greatest Hits (2005), The Collection (2010), and The Essential *NSYNC (2014). The single reached number five on the US Billboard Hot 100.

A Spanish language version of the song, titled "Yo te Voy a Amar" was recorded at the same time and released in Spanish-speaking countries such as Mexico, Colombia, Venezuela, Peru, Chile, Bolivia, Paraguay, Uruguay, Argentina, Ecuador, Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Cuba, Dominican Republic, and Spain. 

Richard Marx was asked by A&R executive David Novik if he had any songs that he could give to NSYNC, which he specifically requested for a ballad.[1] Initially, the song was written with a three-person girl group in mind, which Marx quickly finished after writing the harmonies specifically for NSYNC.[1]

Marx would later record the song twice, first for the Japanese release of his album Days in Avalon similar to the NSYNC version, and again as a rock song for the European version of his Stories to Tell album. Marx would later use the Days in Avalon version of "This I Promise You" for his Now and Forever: The Ballads album as a duet with Asian singer Sabrina.