This book argues that progressive rock is the most concentrated expansion of form in the history of popular music. The book traces the ways in which folk, blues, jazz, psychedelia and classical music of the 1960s were drawn together by progressive musicians, against a backdrop of technological innovation. Progressive bands of the early- to mid-1970s featured complex instrumentation, extended tracks, and album-length concepts. But rather than pigeonholing progressive rock, the authors explain its diverse roots and argue that a fusion of musical styles and approaches defined the 1970s even after the assault of punk. These connections are grounded by close analysis of albums and key tracks, and an examination of performance and cultural contexts. The authors show that "progression" underpins many subgenres of rock, including major progressive albums and bands of the 1970s, alongside neo- and post-progressive musicians from the 1980s to the 2000s. Featuring artists as diverse as Marillion, Kate Bush, Talk Talk, Radiohead, The Mars Volta, Porcupine Tree and Midlake, this book is ideal reading for anyone interested in the history and meaning of progressive rock in all its forms.