This book combines expertise in different fields, including biotechnology and electrical and electronic engineering. The biological signals are usually dedicated to a specific frequency range or a specific voltage range. As engineers, we need to think about how to capture disturbed or noisy biomedical signals and convert them into meaningful biosignals. This intermediate process includes signal amplification (amplifier design), noise removal (filter design), analog-to-digital conversion (analog-to-digital converter design), digital signal processing (algorithm design), and data transmission through human–machine interface (interface circuit design) or wirelessly (frequency synthesizer design, radio frequency circuit design). All these topics belong to electronic engineering. Information brought by biological signals can be used for many applications. For example, rehabilitation aids or equipment can be manufactured through a human–machine interface to improve the quality of life. The implanted devices also allow the patient to immediately apply appropriate feedback, such as cochlear implant to stimulate the auditory nerve or pacemaker to stimulate the heartbeat. These signals can also be wirelessly transmitted to a medical center or emergency center to notify relevant units of immediate responses and preparation so that patients can receive treatment and immediate care.