Tonality during the common-practice era carried conventions that ultimately manifested formal schemas. Post-tonal composers’ diverging treatment of form escapes the generality of such schemas, and the relative lack of formal methodology for post-tonal music has left a considerable gap in the literature. When writers do discuss form in post-tonal music, the discourse generally focuses on form within a single composition, a single composer’s output, or at best a narrow school of musical style or philosophy. This thesis posits a concept that I call formal synthesis as a basic principle of form applicable to a broad range of musical styles, genres, and eras. Formal synthesis is a process that combines two or more previous musical passages into one musical passage. This organizational principle covers a broad spectrum of formal possibilities, varying by formal function, structural level, and method. In chapter one, I summarize previous discussions of form in post-tonal music and define the categorizations of formal synthesis. The following chapters refine the concept of formal synthesis through analyses of Steve Reich’s Drumming, Béla Bartók’s Piano Suite op. 14, and Thomas Adès’ Asyla. These composers belong to three different generations and nationalities, and the pieces belong to distinct styles and genres.