This Report provides guidance to designers and developers of carbon capture and storage (CCS) systems with all, or portions, of the system located underwater. Subsea CCS projects are new and no standards or clear regulations for their design exist. This Report is intended to help designers evaluate key decisions and mitigate risks unique to a subsea CCS system. Additionally, the document refers to other documents that will aid in specification and design of a subsea CCS system. Unique aspects of subsea CCS systems are highlighted and recommendations or options to address design decisions are offered.