Book excerpt: This second edition of Amikam Aharoni's Introduction to the Theory of Ferromagnetism is a textbook for first year graduate and advanced undergraduate students in physics and engineering as well as a reference book for practising engineers and experimental physicists who work in the field of magnetism. For this edition, the author has updated the material especially of chapters 9 ('The Nucleation Problem') and 11 ('Numerical Micro-magnetics'), which now contain the state of the art required by students and professionals who work on advanced topics of ferromagnetism.