The mission of the Material Data Hub is to provide a public-facing FAIR Digital Object Repository for storing experimental or simulated data and metadata, enforcing materials specific schemas, and sharing a common materials vocabulary. The repository supports linking data, which can relate objects in the repository to each other or to the other available materials repositories such as Aflow, Materials Project, OQMD, and others. While we are specifically targeting material microstructure and process-structure-property relationships, this repository is open to broad contributions from the materials science and engineering community. The development of this portal is led by the Georgia Institute of Technology, and the National Institute of Standards and Technology. This development responds to the NSF-Sponsored Report on Materials Data Infrastructure (MDI), and two NSF-Sponsored microstructure repository workshops led by Lehigh University and the National Institute of Standards and Technology. The Material Data Hub implements the best practices and minimum metadata requirements identified during the microstructure repository workshops.