This chapter explores the concept of a data ecosystem, wherein data from various domains, such as community-building, transportation, and energy, is utilized to enhance smart cities. By sharing and interlinking data across multiple sectors, new businesses can emerge, establishing data as a pivotal asset for sustainable urban development. The chapter explores the infrastructure needed to support this data ecosystem, including networks, data storage platforms, and marketplaces. Through real-world examples and case studies, readers will gain insights into how data can be leveraged to improve services, reduce costs, and generate new value in smart cities. Section 10.1 explores the utilization of data as a new community resource in smart cities. In Sects. 10.2 and 10.3, the concepts of a data ecosystem and its data infrastructure are explained. Section 10.4 outlines various measures and functions designed to promote data use. Section 10.5 discusses the challenges and impediments identified through a study conducted in Kashiwa-no-ha Smart City. Section 10.6 examines how data-driven decision-making processes can enhance urban management and services. Finally, Section 10.7 outlines the future prospects and potential challenges of implementing data ecosystems within smart cities.