The Modern Era (1900 - 1945) - The Conservatory at Humanities Web outlines the rise of post-romantic music, rhythmic, harmonic, and tonal experimentation, and lists major composers with biographies, suggested reading, and additional resources.
20th Century: 1900-Present - Introduction to recent compositional work from Essentials of Music. Linked to details on historical themes, musical context, style, and living or recently deceased composer biographies.