The city of Stockholm has set the goal to build 140 000 new residential units by 2030 to meet the demand of a growing urban population. Simultaneously we are seeing a decline in biodiversity in and surrounding the city. Some of the main factors are climate change, pollution, overexploitation and habitat destruction. As cities grow, they have the potential to aid or accelerate these problems, depending on how this urban growth is approached.In current urban development projects in Stockholm, we increasingly see large scale, high exploitation projects that view efficiency and profitability as their main goal. Biodiversity is largely considered an afterthought. We are chipping away at natural habitats and infrastructure, which has dramatic consequences for other species and ultimately ourselves.This thesis is a study on the city’s impact on biodiversity, and how new developments in Stockholm relate to our surrounding ecosystems. It is an investigation of how we, as urban dwellers, can live with nature. It is also an exploration of how we, as architects and urban planners, can shape cities for urban mutualism.