This book provides a comprehensive exploration of electrocardiography (ECG) from both clinical and engineering perspectives. It discusses the physiological foundations of cardiac electrical activity, principles of ECG signal acquisition, and advanced techniques for signal processing and analysis. The text integrates theoretical concepts with practical applications, highlighting modern developments such as artificial intelligence, wearable devices, and telemedicine. Designed for biomedical engineers, researchers, and clinicians, it bridges the gap between medical science and technological innovation, emphasizing diagnostic accuracy, system design, and the future trends shaping cardiovascular monitoring and healthcare technology.