The imperatives of environmental sustainability, poverty alleviation and social justice (partially codified in the Sustainable Development Goals or SDGs) call for ambitious societal transformations. As such, few aspects of actionable knowledge for sustainability are more crucial than those concerning the processes of transformation. This article offers a brief overview of different conceptualisations of transformation, and outlines a set of practical principles for effective research and action towards sustainability. We review three approaches to transformations, labelled: 'structural', 'systemic' and 'enabling'. We show how different ways of understanding what we mean by transformations can affect what actions follow. But these approaches are not mutually exclusive. We use an international set of examples on low carbon economy transformations, seed systems, wetland conservation and peri-urban development to show how they can be complementary and reinforcing. We describe three cross-cutting practical considerations that must be taken seriously for effective transformations to sustainability: diverse knowledges, plural pathways and the essentially political nature of transformation. Realizing the ambitions of the SDGs, we conclude, requires being clear about what we mean by transformation, and recognizing these basic methodological principles for action.