Since Donald Griffin first used a heterodyning circuit to listen to the echolocation calls produced by bats, the equipment used by bat workers to study biosonar has changed considerably. We are now able to record and analyze biosonar signals in the field, often in real time, using a variety of equipment and techniques. With the application of new methods, such as artificial neural networks and synergetic pattern recognition algorithms, the accuracy of quantitative acoustic species identification systems is also improving steadily. However, field-workers must still choose the most appropriate equipment for the task at hand. Expensive equipment can perform a wider variety of tasks, but simpler, cheaper, and more rugged equipment may be more appropriate (table 62.1). This equipment must also be used properly, and studies designed and carried out correctly, in order to obtain the most accurate results possible. The production, transmission, and receipt of sound is still subject to the laws of nature; thus, the problems associated with recording and analyzing ultrasound, such as atmospheric attenuation, remain. No technological development can relieve the observer of the necessity of having knowledge of acoustics and bat ecology. Otherwise, the interpretation of results could be erroneous.