Perioperative fluid therapy remains a highly debated topic. Its purpose is to maintain or restore effective circulating blood volume during the immediate perioperative period. Maintaining effective circulating blood volume and pressure are key components of assuring adequate organ perfusion while avoiding the risks associated with either organ hypo- or hyperperfusion. Relative to perioperative fluid therapy, three inescapable conclusions exist: overhydration is bad, underhydration is bad, and what we assume about the fluid status of our patients may be incorrect. There is wide variability of practice, both between individuals and institutions. The aims of this paper are to clearly define the risks and benefits of fluid choices within the perioperative space, to describe current evidence-based methodologies for their administration, and ultimately to reduce the variability with which perioperative fluids are administered. Based on the abovementioned acknowledgements, a group of 72 researchers, well known within the field of fluid resuscitation, were invited, via email, to attend a meeting that was held in Chicago in 2011 to discuss perioperative fluid therapy. From the 72 invitees, 14 researchers representing 7 countries attended, and thus, the international Fluid Optimization Group (FOG) came into existence. These researches, working collaboratively, have reviewed the data from 162 different fluid resuscitation papers including both operative and intensive care unit populations. This manuscript is the result of 3 years of evidence-based, discussions, analysis, and synthesis of the currently known risks and benefits of individual fluids and the best methods for administering them. The results of this review paper provide an overview of the components of an effective perioperative fluid administration plan and address both the physiologic principles and outcomes of fluid administration. We recommend that both perioperative fluid choice and therapy be individualized. Patients should receive fluid therapy guided by predefined physiologic targets. Specifically, fluids should be administered when patients require augmentation of their perfusion and are also volume responsive. This paper provides a general approach to fluid therapy and practical recommendations.Anesthesiology Department, Botucatu Medical School University of Sao Paulo State - UNESP, District of Rubiao Junior s/n, Botucatu, Sao Paulo, 18618-970 Brazil.Valley Anesthesiology Consultants, Ltd., Department of Anesthesia and Perioperative Medicine, Banner Thunderbird Medical Center, Banner Health, Glendale, 85306 AZ USA.Laboratory of Anesthesiology LIM08, Medical School - University of São Paulo, São Paulo, 05508-070 São Paulo Brazil.Department of Anesthesiology & Perioperative Care, University of California, Irvine, 92697 CA USA.Department of Anesthesia and ICM, University of Udine, Udine, 33100 Italy.Department of Anesthesiology, Duke University Medical School, Durham, 27710 NC USA.Resuscitation Research Laboratory, Department of Anesthesiology, University of Texas Medical Branch, Galveston, 7755-0801 TX USA.Medicine and Physiology, McGill University, Montreal, H3A 0G4 QC Canada.University College London Hospital, 235 Euston Road, Fitzrovia, London, NW1 2BU UK.Department of Anesthesiology and Intensive Care, Sheba Medical Center, Tel Aviv University, Aviv, 52621 Israel.Center of Anesthesiology and Intensive Care Medicine, Hamburg Eppendorf University Medical Center, Hamburg, 20246 Germany.Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, 15213 PA USA.Anesthesiology Department, Botucatu Medical School University of Sao Paulo State - UNESP, District of Rubiao Junior s/n, Botucatu, Sao Paulo, 18618-970 Brazil.