The first thorough theoretical study of Janacek's compositions, focusing on motivic and rhythmic structure and identifying elements that give the music coherence, character, and interest. The works of Leos Janacek, including Jenufa and several of his other operas, have been widely performed in recent years. But they have rarely been investigated closely from a theoretical perspective, and their musical language remains only partially understood. Zdenek Skoumal here offers a chronological exploration of Janacek's compositions that focuses on musical structure, identifying elements and processes that give the music coherence, character, and interest. Skoumal demonstrates how the music combines and blends traditional tonal elements, folk-influenced features, and techniques that were forward-looking at the time. In particular, the music is shown to employ highly sophisticated and continually transforming motivic and rhythmic components. The book's numerous musical analyses are motivically centered and employ various analytical approaches, including ones that involve reduction, structural levels, basic set theory, and rhythmic theory. Discussions of Janacek's works with a libretto or other type of text consider relationships between word and music, revealing their connection to deeper structural issues. The companion website https://zdenekskoumal.wixsite.com/janacek features audio versions of most musical examples, as well as material not included in the book.