Historically the understanding and appreciation of cinema have been shaped by a bias towards the image. Consequently, film sound has received little attention: today we know very little about how sound works in the cinema, especially in contemporary terms. My particular concern is to provide a first substantial account of sound in contemporary Hollywood cinema. Since the arrival of Dolby technologies in the early 1970s, the seismic nature of the changes that have taken place in mainstream cinema are so pervasive as to suggest that we are indeed in a new 'era' of cinema, the Dolby era. This period in the history of cinema has been characterised by a variety of factors such as the emergence of a new generation of filmmakers as well as a new 'kind' of audience. The thesis investigates these changes and their implications within a historical framework that has its roots in the 1960s, exploded in the 1970s, and matured beyond expectations over the past two decades. The thesis is structured around an exploration of the central features and figures that have characterised the Dolby era. It includes an examination of the reasons behind the success of Ray Dolby and Dolby Laboratories, as well as an analysis of the impact that technological innovations in film sound have had on filmmaking practices and the industry at large. The thesis advocates a move towards closer dialogue and integration between the world of academia and that of practitioners by focussing specifically on professional practices through a series of interviews with leading Hollywood practitioners. Finally, the thesis proposes an original approach to some key areas of film studies, namely film audiences, film narrative construction and film analysis.