Biomedical Engineering in the 21st century covers a wide variety of subjects. This book can be viewed as a reference book over some selected topics. For over 40 years the author has conducted research and development on basic topics such as, bio-electric potentials, ECG, EMG, and EEG measurements, blood pressure and flow measurements, pacemakers, medical ultrasound measurements, the cochlea and hearing mechanism. This book reports on such selected topics. A total of seven topics are included in this book. Each topic reports on some elementary physiology concerning the subject matter, with some additional theoretical analysis. Furthermore, some instrumentation and technique used to perform the measurements. With this book I hope to inspire biomedical engineers to become inventive in developing ideas which can help humanity. The human spirit will never stop innovative ideas in science and engineering.