This site offers an introduction to classical music built around Sony's Essential Classics music series. It features Eras , Composers , and a Glossary . Eras covers the six main periods in classical music history, discussing historical themes, musical context, style, and major composers. Composers includes brief biographies and works of nearly 70 composers. Glossary provides 200 terms with examples (recordings or pictures). It also includes almost 200 excerpts from the series in RealPlayer format. From the W.W. Norton & Company and Sony Classical Music.