A key objective of SOOS is the design of a multidisciplinary and sustainable observing system. Given the scale of the Southern Ocean, and the costs and logistical demands associated with making observations, we simply cannot observe all parameters. We need to select those parameters, or Essential Ocean Variables (EOVs) that will provide us with the information needed to detect, track and attribute (either directly or using models) change in the physical, biogeochemical and biological systems of the Southern Ocean. Identification of the EOVs required to provide this information is a difficult task, and must also take into account the feasibility of observing each EOV,and the technology or observing platform required to take the measurement.