Marine Spatial Data Infrastructure (MSDI), the extension of terrestrial Spatial Data Infrastructure to the marine environment, is a type of cyberinfrastructure that facilitates the discovery, access, management, distribution, reuse, and preservation of hydrospatial data. MSDIs provide timely access to data from public and private organizations of marine related disciplines such as hydrography, oceanography, meteorology and maritime economic sectors, to be used for applications such as the safety of navigation, aquatic and marine activities, economic development, security and defence, scientific research, and marine ecosystems sustainability. This chapter discusses the main pillars of a MSDI, its importance for facilitating public processes such as Marine Spatial Planning and Coastal Zone Management, the wide range of stakeholders, implementation challenges, and future developments, such as the FAIR design principles, new data sources and services.