California has historically provided a fertile breeding ground for radical modes of architectural thinking, practice and building, which from the 1920s onwards was sparked by the presence of eminent émigré architects. It was also central to the birth of ‘cool’ mid-century Modernism – all in parallel with the intense concentration of design and experimentation in the film, aerospace and tech industries. This AD issue explores the influential formal tropes generated in the nexus between Los Angeles and the Bay Area, as well as the thriving theoretical preoccupations that have brought California's architects global attention. Between Hollywood and the Silicon Valley, this unique context has nurtured and become the platform for those who not only build buildings around the world, but have also founded and directed schools and educated emergent generations of architects