This is a single textbook covering the subject matter of Circuit Theory that helps undergraduate students of engineering in solving many technical design problems arising in electrical, electronics, large-scale systems, computers, communication systems, measurements and instrumentation. The book has been prepared to cover the entire syllabus of 'Circuit Theory', which is common to BE in ECE, EEE, EIE, ICE, BME and Medical Electronics branches. Each chapter of the book begins with a brief introduction and ends with review questions and numerous practice problems. After discussing the foundations of circuit theory, the book describes the network reduction techniques and various theorems used in analyzing the DC and AC circuits and goes on to describe resonance and coupled circuits, transient response and two-port and threephase circuits. The hallmark of this book is the numerous solved problems, a wide variety of which will help the students to gain sound knowledge and fully internalize the concepts of circuit theory. These have been worked out with step-wise solutions. Illustrations are clear and text has been kept simple.