This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book sets out to explore a Broadway show that is often seen as a turning point in the history of musicals and discusses the musical manuscripts. It examines aspects of Bernstein's musical language, first in broad terms, and with reference to individual musical numbers. The book provides an account of the original Broadway cast recording, a copy of which is also included on the accompanying compact disc. A substantial part of the monograph is the result of a study of the magnificent collection of primary source material in the Leonard Bernstein Collection in the Music Division of the Library of Congress. Anyone writing about Bernstein owes an enormous debt to Humphrey Burton's Leonard Bernstein, a biography that is as scrupulous as it is entertaining and which contains a wealth of information not to be found elsewhere.