This thesis focuses on the new algebraic structure: semi-brace. We study basic properties of this structure and we show that semi-braces are a generalization of braces. Moreover we introduce new constructions of semi-braces, the asymmetric product and the matched product, in order to obtain several examples of semi- braces. Finally, we prove that we may construct left non-degenerate solutions of the Yang-Baxter equation through left semi-braces.