Observing behaviour of individuals is often limited for free-ranging animals. Biologging, a method recording a variety of parameters using animal-borne data loggers: body acceleration, horizontal position, magnetic field, pressure, video footage etc., has enabled us to reveal unobservable behaviour of animals at fine-large spatial/temporal scales. Also, acknowledging recent success in miniaturization of devices (ca. 1g), this method is now applicable to a wide range of animal taxa, though Biologging has been dominantly used for species in marine habitats including marine mammals, seabirds, fish. On the other hand, deployed animals can be used as a sufficient monitor for environments, such as ocean currents, water column structure, wind velocity, and also environmental pollution. Furthermore, changes in distribution and/or behaviour of top predators reflect ecosystem dynamics in response to varying environmental conditions. In this presentation, we introduce recent biologging studies and also collaborative works with other study areas, e.g. physiology, genetics, and information science, especially in seabirds, and discuss a future direction of Biologging.