Biodiversity in the Netherlands has been under alarming pressure for many years. Historical drivers of biodiversity loss have been agriculture and urbanization, through causing environmental pressure, loss of natural habitat and fragmentation of habitat for numerous species and ecosystems (PBL, 2014). Pressure on biodiversity remains high today as the limited amount of land in the Netherlands is used intensively and densely inhabited.  Biodiversity ensures the health and resilience of ecosystems (Vink, Vollaard & de Zwarte, 2017): it influences its functioning and ability to react and adapt to changes. People are dependent upon the world’s ecosystems through the ecosystem services they provide, but at the same time their actions are affecting the health and resilience of these ecosystems in a negative way. This relationship has to change fundamentally in order to ensure a healthy future for the worlds ecosystems and each species involved. Although biodiversity is generally higher in cities than in the rural areas around (Pötz, 2016; Vink, Vollaard & de Zwarte, 2017) many species are still under pressure. There is a lack of biodiverse and connected green spaces, disturbances such as light and maintenance are negatively affecting urban ecosystems and nesting opportunities for species that have become dependent upon the city are disappearing (Dramstad, Forman & Olsen, 1996; Vink, Vollaard & de Zwarte, 2017; CBS, PBL, RIVM, WUR, 2018). This in turn also negatively affects the ecosystem services available for people living in cities. Future urban development, such as inner-city densification, are expected to further contribute to these pressures, as nature is still largely excluded from urban planning and design processes (Snep & Opdam, 2013, Pötz, 2016; Vink, Vollaard & de Zwarte, 2017; Weisser & Hauck, 2017). This graduation project researches how knowledge from biodiversity, urban ecology and nature-inclusive design can be translated to urban planning and design. This is done by researching theory and at the same time studying the spatial aspects within the case study location of the Zomerhofkwartier in Rotterdam. The aim is to reach mutualist urbanism: a way of urban planning and design that provides conditions for strengthening biodiversity within ‘habitats’ that will also benefit people greatly. The found methods for a mutualist urban planning and design process consist of facilitating an ‘interwoven urban mosaic through strongly interconnected landscape elements’ (Forman, 2014) by designing for animals and people simultaneously (target species and target groups). Design principles that are then applied in design are: use, 3d connectivity, porosity, microclimate and time. Using these methods and design principles four mutualist habitats are designed for the Zomerhofkwartier that integrate within the ecological network of Rotterdam: a multi-level street, a public courtyard, a collective rooftop network and a collective garden. These mutualist environments provide a new relationship between the city and urban nature, between built structures and urban nature and between people and urban nature.