Premised on the underlying principles and aims of the Picturesque in architecture—among them, the grounding of a house within its surrounding landscape, a greater eclecticism of style and embrace of asymmetry, an emphasis on views and view-points, a concern with issues of framing and movement and a re-examination of the relationship between the natural and built environment—this dissertation examines some of the physical, three-dimensional repercussions of those ideas on the design and execution of British country houses at the turn of the nineteenth century. It departs from previous scholarly approaches in its focus on specific architectural responses and solutions that mediated the relationship—boundaries, transitions and interactions—between house and garden, and how those solutions contributed to addressing issues such as grounding, framing, access and movement. Looking closely at the work of three leading architects of the period—James Wyatt (1746–1813), John Nash (1752–1835) and John Soane (1753–1837)—it examines how each harnessed the specific qualities and challenges of a building site in light of those concurrent theoretical and aesthetic concerns. Relying primarily on detailed examination of surviving architectural drawings, related archival materials and extant houses, the analysis is divided into three main areas: the presence (or absence) of level changes or stepped floors within the principal floor of the house and between the house and garden; the increasingly permeable boundary between interior and exterior, including the use of full-length windows and French doors, loggias and verandas and, above all, glass conservatories; and a more specific focus on the attached conservatory—its origins, popularity, forms and roles—as a fully integrated social-botanical space directly accessible from other polite rooms and central to the life of the household.