These lecture notes originated in a seminar on Model Theory that I gave in the academic years 2005–06 and 2006–07 at the Department of Logic, History and Philosophy of Science of the University of Barcelona. I had presented some previous work on the basic notions of simple theories in July 2002 in the Simpleton Workshop held at the Centre International de Rencontres Mathématiques, Luminy (Marseille), which was subsequently published as [8]. A more extended version, including the exposition of stable theories, was the topic of a tutorial entitled Advanced Stability Theory that I taught in the Modnet Summer School that took place at the University of Freiburg in April 2006. And in preparing the material, I also drew on some courses on these topics given at the Universidad de los Andes, Bogotá, in August 2000 and in August 2004.

The notes are based on the work of many model theorists. The names of John T. Baldwin, Ehud Hrushovski, Byunghan Kim, Daniel Lascar, Ludomir Newelski, Anand Pillay, Bruno Poizat, Saharon Shelah, Frank O. Wagner, and Martin Ziegler deserve special mention. I learned stability theory from Martin Ziegler and I have made as much use as I could of his short and elegant proofs, presented in his courses and in his unpublished lecture notes.

This book is not as ambitious as Frank O. Wagner's book on simple theories [41], but its pace might be more comfortable for the beginner.