This book includes a selection of reviewed and enhanced contributions presented at the SpaceOps 2021, the 16th International Conference on Space Operations, held virtually in May 2021. The chapter selections were made based upon their relevance to the current space operations community. The contributions represent a cross-section of three main subject areas: Mission Management – management tasks for designing, preparing and operating a particular mission; Spacecraft Operations – preparation and implementation of all activities to operate a space vehicle (crewed and uncrewed) under all conditions; and Ground Operations – preparation, qualification, and operations of a mission dedicated ground segment and appropriate infrastructure including antennas, control centers, and communication means and interfaces. The book promotes the SpaceOps Committee mission to foster the technical interchange on all aspects of space mission operations and ground data systems while promoting and maintaining an international community of space operations experts.