An excellent
introduction to
Mathematical finance and it is very usefull text for introductory course in mathematical finance.
This book suited for self study, that is the presentations style, examples and excercises are very good. If you look at the book which start from
introduction probability theory , then go long away to understanding brownian motion. After defining brownian motion the book teach you pricing simple financial derivatives. The book contains the derivations and examples. Also discuss brownian motion with jump and pricing the exotic contract. Also convers optimization theory and utility theory which is very important for finance and economics.