This commentary discusses the role of social and solidarity economy (SSE) in the implementation of the Sustainable Development Goals of the UN. The fast pace of urbanization has caused many social and environmental problems to our planet. Instead of following the profit-maximization approach for development, SSE is regarded as one of the solutions to address the issues. This commentary introduced the characteristics of SSE and its tendency to address social and environmental issues effectively due to the people-centred and integrated approach. In the second part of the commentary, the City of Seoul is used as an example to showcase how social economy can be implemented, its achievement and contribution to the society, and the difficulties for the expansion of SSE in competition with the market economy.