Bats evolved to fly in the dark and developed echolocation to navigate in these conditions. Even though we cannot hear their acoustic emissions, we can record and analyse them with appropriate equipment and software. The author acquired unique knowledge and skills over more than three decades of continuous research on bat ultrasonic emissions. In this book he uses here advanced computer-assisted analysis to supplement the auditory approach to ultrasound analysis he initially developed in France. The method described makes it possible to identify about 85 % of bat acoustic records in Europe and to carry out non-invasive bat assessments and in-depth surveys. Thirty-five of the 42 bat species present in Europe are covered. The book also includes access to more than 300 downloadable files online that can be used to practice and develop skills in identifying bats by their sonar signals.