This E-book is filled with information to give lecturers and students a ready reference and instructional material in Fundamental of AC theory and Circuit Law in AC system. The layout of this e-book is designed to assist the lecturers that is new to this subject and the students to learn by themselves though presentation notes and the videos in this subject for a better understanding. The e-book is written in simple yet structurally manner for easy learning and understanding the subject. This E-book will become a good instrument and reference for learning and teachings session and relevant in instructional planning lecture management and decision making.