This report aims to initiate a process that will ultimately result in a more comprehensive, coordinated, and integrated cryospheric observing system. The report starts with an Executive Summary that includes major recommendations. Chapters 1 and 2 define the cryosphere and the major applications of cryospheric data. Chapters 3-10 describe our current capabilities and requirements for observing essential climate variables (ECVs) in the major domains of the cryosphere. Each of these chapters contains domain-specific recommendations. Chapter 11 reviews the cryospheric observing system by observation types

i.e., in situ, satellite, and airborne. Data management objectives are detailed. Chapter 12 presents the Theme implementation considerations and their timeline. Throughout the report we will refer to the Cryosphere Theme as CryOS, the Cryosphere Observing System.