This second edition updates the well-regarded 2001 publication with new short sections on topics like Catalan numbers and their relationship to Pascal's triangle and Mersenne numbers, Pollard rho factorization method, Hoggatt-Hensell identity. Koshy has added a new chapter on continued fractions. The unique features of the first edition like news of recent discoveries, biographical sketches of mathematicians, and applications - like the use of congruence in scheduling of a round-robin tournament - are being refreshed with current information. More challenging exercises are included both in the textbook and in the instructor's manual.