Obtaining new information on the natural world involves direct observation, measurement and experimentation. However, this can be challenging for species that are very small, cryptic, sensitive, fragile, rare, dangerous or live in extreme environments. As a result, information on the life history, behavior, physiology, and ecology of many animals is scant or non-existent. The scientific field of bio-logging has existed for many years, but recent advances in electronic miniaturization and digital information processing and storage are providing new insights into the hidden lives of animals that can only be studied vicariously, that is, indirectly through the use of technology. Bio-logging generally involves an animal- borne instrument that monitors or records aspects of an animal's biology (e.g., behavior, movements, physiology) and its environment. For example, bio-logging instruments can record video or still images of animal behavior and record data from a variety of sensors that monitor location and locomotion (three-dimensional movement), physiology (body temperature, heart rate, blood oxygen concentration), and environmental variables (ambient temperature, light level, oxygen concentration, salinity, sound). This information is either stored for later recovery or transmitted immediately. In many cases, the initial challenge is locating the species, then attaching and recovering the instruments. However, as bio-logging technology becomes smaller and more data rich, we face the challenge of storing, classifying, analyzing, integrating, and disseminating the data and results. New methods of analysis will be necessary to handle the staggering volume of information. Creating data rich, virtual worlds in which to view and integrate data will require advanced computing capability. Data sharing and dissemination will enable broad collaboration, validation and interpretation of complex systems that attempt to understand, model and predict how animals function and interact with their environment at micro and macro scales and over time periods of seconds to centuries. The scientific field of bio-logging will provide basic knowledge on the function of free- ranging organisms at the individual and community level that will be needed to manage and conserve species and their habitats and to mitigate human impacts.