Twentieth-century Australia saw a multiplicity of expressions of modernity and fashionability in interior design, yet narrowly defined historical views of the aesthetics of the modern interior have left the majority of practices during the post-war boom undocumented. The study investigates the work of Noel Coulson and Decor Associates, two Australian interior designers working in the post-war period. This thesis, drawing on the work of French sociologist Pierre Bourdieu and developing concepts derived from British design historian Penny Sparke, analyses these practices and six client case studies through its two key themes of hybridity and modern not modernist. The two designers, it is argued, are exemplars of hybrid practitioners who acted as both producers and mediators. The client case studies expand the theme of modern not modernist – interiors whose modernity is defined by lifestyle and expression of identity. This thesis concludes that recognition of the role of the client is fundamental to exposing the hybridity of the designers’ practices and the diversity of the aesthetics of the modern interior. The findings support the validity of the two concepts in understanding the significance of previously overlooked design styles, contesting their historical relegation and re-evaluating their capacity for expansion of the historical field. This thesis proposes that the two key themes offer a new framework to re-examine the work of interior designers currently omitted from design history.