There are as many perspectives in designing as there have been instances in which it has occured. In each instance, constraints will have invariably arisen in various forms, to the extent that designing and constraints are considered to be an inherently natural pairing. In addition, they are both affected by the challenges of complexity, amongst many others, which is especially compounded by an increasingly significant shift towards interdisciplinary methods and means of working. This has been in response to the influences and implications with regards to the integrated elements of sustainability and sustainable development. To this effect, the body of research effort presented in this thesis searches for a simpler perspective towards designing, to which constraint-based thinking can be applied. It explores the implications of interdisciplinarity in the context of sustainability and sustainable development. It also considers an example of design-based process within the built environment that is inclusive of multiple disciplines and therefore not only interdisciplinary, but also affected by complexity. In response to these instances of complex interdisciplinary designing, this thesis contributes an exploration of constraint-based thinking and the consideration of an approach which uses design objectives as optimisation constraints, from which a methodology has been created. Furthermore, this thesis demonstrates constraints as useful in understanding, especially in the context of problem structures and their respective design spaces. As a form of constraint, optimisation objectives are also presented in this thesis as a means of exposing and handling complexity when applied as constrained optimisation for focusing designing efforts. Above all, this thesis advocates the use of constraint-based thinking and simplicity towards enhancing and supporting designing process.