This thesis comprises two related aims. The first is to define the identifying features of an artistically progressive popular music. The second is to use this definition to critically consider the canon of progressive rock, exploring its position as an artistically progressive musical style and considering how this quality changed over time. This thesis explores two discourses by which to define artistically progressive as it relates to popular music. The first is G.W.F Hegel’s depiction of the dialectic: the synthesis of two opposed forms (a thesis and antithesis) that is persistently rechallenged by new antithetical forms hence, thereby motivating its course inexorably forward. The second is the ideology of modernity, self-consciously striving for self-negation and avoiding repetition and stagnation at all costs. The term artistically progressive is used so as to differentiate the particular quality sought in this thesis from any other potential meanings of “progressive.” This thesis is interested in progressiveness as it relates to the artistic (compositional and creative) texts of the bands and musicians analysed, thereby linking popular music to the idea of progress in art history discourse. It is therefore a principally musical and paramusical study, analysing a broad range of music encompassing before and beyond the progressive rock canon. Moreover, it endeavours to pair this musical analysis with discussion of social, cultural, and historical context chiefly through the analysis of contemporaneous journalistic media in order to provide insight into the ideals and ambitions which drove the changes in the musics analysed. This study commences before progressive rock, considering the trajectory which led to the “proto-progressive” music of the mid/late-sixties. This trajectory begins with the advent of rock and roll, an industry-dominated music which was reoriented, primarily by the success of the Beatles, to the performative domain of the youth themselves. As the Counterculture became a widespread youth movement in the mid-sixties some of this music was shaped around its proclivities: enigmatic, sophisticated, complex. Artists and journalists began to invoke the term “progress” as a laudable ideal underpinning their increasingly diverse artistic project, one which foregrounded artistic sovereignty, sought artistic legitimation, and which was purportedly opposed to commodity. The music which developed in this context and which challenged various aspects of contemporaneous pop music – the likes of the Beatles, the Beach Boys, Pink Floyd, Procol Harum, Frank Zappa, the Moody Blues, and others – was tremendously heterogenous, expressing its experimental ideals along myriad parallel stylistic trajectories. It is hypothesised that this was the first artistically progressive popular music: one invested in change and self-negation and one driven by ideals of artistic expansion. By the early-1970s the exploratory rock music developed throughout the previous decade had become enormously commercially successful and its biggest exponents – Yes, ELP, Jethro Tull, Genesis, and others – came to define progressive rock as a genre. This was the crystallisation of progressive rock: the shift from a popular music movement definitively diverse and compelled by artistic conceits to one adherent to an increasingly specific aesthetic. Furthermore, although the progressive rock style (although not all of its biggest artists) waned in popularity in the late-seventies, it was revived in the eighties by neo-prog bands like Marillion, Twelfth Night, Pallas, and others, who brought progressive rock to a new generation of fans. In the hands of these bands, progressive rock was consolidated – its stylistic compass was reduced as they promoted the sounds of their key influences. This process is perpetuated, too, by bands like Dream Theater in the present. It is therefore hypothesised that progressive rock, as it is conventionally conceived, has demonstrated less artistic progressiveness over time and has been driven by an increasingly conservative stylistic motivation as it has been exposed to further generations of reification. However, it is proposed that there has always persisted a small contingent of rock artists perpetuating the artistically progressive quality earlier defined irrespective of time and connection to the progressive rock canon. Two artists theorised to embody this quality are Radiohead (not conventionally considered to be progressive rock) and King Crimson (conventionally considered to be progressive rock). Both appear to embody a modernistic vision towards self-negation, and both seem also to exist in a state of continual stylistic flux, challenging their prior musical directions, their surrounding musical style, and popular music’s conventions. They are therefore theorised to be artistically progressive rock acts.