This thesis focuses on two main themes in the architectural history of the country house in Wales, investigating firstly its development, and secondly some of the distinctively Welsh features of these houses. It argues that both themes have been marginal in recent historiography of Welsh architecture, culture and society. In this work, houses owned by families of Welsh descent are discussed to ascertain whether ethnicity and nationhood are actually identifiable in the architecture. Critical analysis of built fabric is supplemented and supported by primary sources such as the poetry of the bards, building accounts and records, architectural drawings, travel journals, photographs, works of art and a variety of secondary sources. In this thesis, it becomes apparent that one of the most distinctive features of country houses in Wales is the unit-system. This form of dual planning is a peculiarly Welsh feature, enabling two ‘households’ to co-exist simultaneously, adjacent to each other but not necessarily physically connected. Such forms of building are absent from most regions of England, and its presence here is due to differences in the development of the Welsh family. The existence of a different legal system and associated customs in Wales, such as the prominence of gavelkind and female inheritance, are thus expressed in physical form. This practice has set a precedent for design and planning which has influenced a distinctly Welsh country house plan, based not only upon the need to accommodate several family members but also on a desire to preserve the domestic property of their ancestors as a physical manifestation of precedency, pedigree and memory. This elevation of genealogy is a defining feature among Welsh gentry families, who distinguished themselves not by wealth but by blood, which in England became reversed. The development of the Welsh country house offered an alternative form of nationalism, which was multifaceted in nature, and formed an essential element of architectural history in Wales.