The world is experiencing climate change. Environmental problems are substantial and it's known that economic growth contributes to them. In addition, social inequality in society has grown. As a response, the concept of sustainable development has come up, but to date businesses find this hard to implement in their ways of working. As societal pressure is increasing, a growing trend can be seen by pioneering businesses, social entrepreneurs and impact investors working towards an impact economy. In the built environment, however, the concepts of ‘impact thinking’ or ‘social entrepreneurship’ are still very much unknown. Although some institutional investors have adopted an ESG-approach for their investments and a number of developers have started to brand themselves as sustainable, to date there is barely no evidence suggesting that this actually leads to positive societal impact. Very few parties in the built environment place impact first in their corporate strategy or measure the impacts they make. As the built environment is responsible for many environmental and social problems, this is something that needs to change. This thesis therefore researches in what ways impact thinking can be implemented into (urban) development, from the perspective of the social entrepreneurial developer. The first part of the research was conducted through a literature study, the second part through a combination of qualitative and design research. A total of 16 interviews have been conducted with impact developers, impact investors and urban development experts. Based on findings, a first definition for impact development is given, its barriers an drivers are formulated and six principles for impact development are proposed. Through a collaborative research through design approach, also an example impact development was designed: a social-impact based plan for the gentrifying neighborhood Wielewaal. The research outcomes aim to inspire private parties in urban or real estate development to place impact first in their ways of working. In doing so, this thesis aims to open the dialogue about the responsibility of businesses to society and our cities and help developers and municipalities work towards more long-term sustainable and fair urban developments. For impact thinking to really take a flight in (urban) development, taxing or incentivizing impact by the government is necessary.