Circuit Theory is intended for engineering students pursuing courses in institutions of higher learning. The book is conceived and designed as a one-semester text on basic circuit theory, in line with the relevant syllabus of the Ministry of Higher Education. The aim of this book is to assist students in understanding the basic concepts of circuit theory and developing the fundamental tools of linear circuit analysis, which will be useful for all engineers. Students will learn about the various components of circuits, including wires, resistors, capacitors, inductors, voltage and current sources, and operational amplifiers. This book is also suitable for students intending to pursue more advanced courses in circuit analysis. The book opens with an introductory chapter on basic concepts, followed by a chapter on basic voltage and current laws. Other chapters cover topics on systematic analysis method, circuit theorem, operational amplifier, capacitors and inductors, first order RL and RC circuit, as well as sinusoidal steady state analysis.