This paper is an overview of the global water cycle issues that the scientific community is faced with resolving to advance our knowledge in this area. It represents a summary of the discussions held as part of the Science Steering Committee of the USGCRP Global Water Cycle Program, as well as of the "Hornberger Report." Among the various topics being covered are (1) global water budget; (2) teleconnections; (3) persistence; and (4) prediction and predictability.