Effective wildlife conservation requires detailed scientific data on the movement, behaviour and physiology of free-ranging animals. Collecting such information through direct observation is challenging, and in many species, simply impossible. “Bio-logging” employs miniature animal-attached electronic tags to uncover the hidden lives of wild animals, including birds, mammals, fish and even insects. Technologies include: satellite tags to chart migration routes; video cameras to film foraging behaviour; and accelerometers to measure energy budgets. These cutting-edge approaches are revolutionising the field of biology, significantly advancing global efforts to understand and protect wildlife.