Capturing the mechanical behaviour of engineered soils requires new constitutive models tailored for stabilising materials (biogenic, polymeric, etc.) and methods for their inclusion in soil. In this book and to accommodate such an integrated approach, a range of non-conventional materials are first discussed from physio-chemo-mechanical, circularity, and socioeconomic perspectives. Contributions continue with tailored methods for the determination of advanced mechanical properties and methods to capture the response of grand systems constituting such materials. The book concludes with contributions about how materials and methods should and are combined to develop new soil models. The integrated approach followed in this book makes it of interest to geotechnical researchers, as well as design engineers, policymakers, and planners—hence the broad spectrum of built environment stakeholders.