This dissertation examines the history of Britain’s security industry, specifically the rise and development of patent lockmaking in England, throughout the “long” nineteenth century as a way of contextualizing the Victorians’ preoccupation with securing property and privacy. “Under Lock and Key” traces this history through discourses that include technical and trade literature, advertising, records of Britain’s main engineering institutions, press accounts of a lock controversy at the Great Exhibition, as well as writing on loss prevention, crime, political economy, and domestic management. While recent critics have concentrated on nineteenth-century privacy, particularly with reference to architecture and dwelling practices, none have given attention to security’s social origins, material conditions, and sociocultural significance—despite the fact that lock and key appear more often in Victorian fiction than nearly any other consumer artifacts of the era. Through readings of literary texts by Charles Dickens, Benjamin Disraeli, Anthony Trollope, Richard Henry Horne, Robert Louis Stevenson, and Sir Arthur Conan Doyle, this study argues that security carried a complex range of social, cultural, and political meanings which were subject to considerable slippage throughout the nineteenth century. On one hand, the invention of patent locks, and other modern security technologies like burglarproof strongboxes and safes, corresponded with the emergence of Britain’s reform culture and the claims of liberal individualism and thus played a crucial role in middle-class efforts to stabilize the physical and conceptual boundaries between the separate spheres and in shaping an array of social codes and cultural imperatives. On the other hand, the proliferation of security encoded anxieties about middle-class life in industrial-capitalist society, and lock and key served as troubled markers of agency, subjectivity, and competing claims of individuality and social responsibility.