Of central importance to this thesis is the way security measures contradict the process through which museums have been seeking to divest themselves of theoretical hierarchies and value judgments in recent years. A context for investigation is established that considers how a perceptible increase in art theft, complicated by the escalating value of individual objects and the proliferation of museums as represented by a rise in attendance figures has produced a climate of vulnerability for arts collections around the world. In response, museums are installing unprecedented levels of security that are having a significant impact on established viewing conditions and redefining museum space. Further hindering this situation is the disparity between the fields of museology and museum security. These two fields have grown simultaneously, yet independently of one another producing a significant paradox between museum rhetoric and practice. To address the disconnection, this thesis seeks to make museum security relevant to academic discourse by aligning features related to the safeguarding of collections with contemporary museological considerations. Taking the void left behind by a stolen object as a point of departure, this thesis examines the ways in which theft alters the relationship between viewer, object and space in the museum setting. Three major case studies each form a chapter exploring the impact of the theft on established viewing conditions. As the first art theft of the modern era, the theft of the Mona Lisa from the Louvre, Paris (1911) creates an historic precedence for this investigation allowing for the examination of how conventions based upon exclusivity were dismantled by the theft, only to be reproduced by a legacy of increasingly prohibitive security measures. The theft of thirteen objects from the Isabella Stewart Gardner Museum, Boston (1990) is used to address the implications of theft on a fixed and introspective collection, and in particular upon institutional identity and public memory. The theft of the Scream and Madonna from the Munch Museum, Oslo (2004) and its subsequent security upgrade reveal a negation of institutional transparency and the birth of a new security aesthetic. An analysis of each space is balanced against material gathered from a variety of visual, textual and ephemeral sources to produce a developed understanding of affected space.