Peri-operative fluid therapy continues to be an exercise in empiricism, with nagging questions about efficacy and complications. Pharmacokinetics is used for studying the time dependency of administered drugs. Volume kinetics is a pharmacokinetic approach describing the peak effects and clearance of intravenously infused fluids. It clarifies the absorption, distribution, metabolism and excretion of an intravenous fluid bolus. This could possibly allow for more rational design of intravenous fluid paradigms to improve clinical fluid therapy. This chapter briefly summarizes currently accepted principles of fluid therapy, discusses the general approach to kinetic analysis of fluid therapy, reviews currently available data defining kinetic responses to fluid therapy, and speculates about future applications of this approach.