Guidelines for Standardization of Bed Rest Studies in the Spaceflight Context, published 2014, 70 pages. Bed rest studies, in which healthy volunteers are confined to bed in a 6° head-down tilt position, are a well-established model for some of the adaptations experienced by astronauts during spaceflight. They are therefore a very valuable tool both for investigating possible mechanisms and for testing measures to counter these adaptations. Further, the results obtained in these studies have obvious relevance and applications in terrestrial clinical contexts, which make them even more useful. Many space agencies (and in some cases even individual investigator teams) around the world are involved in organizing bed rest studies. However the conditions in which these studies are performed are quite diverse. Differences lie, for example, in the duration of studies, angle (6° tilt or horizontal), sunlight exposure, sleep/wake cycles, nutritional standards and control. This complicates drawing overall conclusions and comparing results on countermeasure effectiveness between different studies. In order to achieve better standardization of bed rest studies in the spaceflight context, an International Academy of Astronauts (IAA) study group was initiated, including members from most of the entities that are actively pursuing this type of activity. This cosmic study represents the outcome of the work of the study group. Standardization can be differentiated to two different aspects: standardization of the conditions of bed rest studies and standardization of a core set of measurements to ensure that a minimum of outcome data are available from every study. Consequently this report contains description of these two aspects.