Probability theory as a subject began in seventeenth century in France when the two great French mathematicians, Blaise Pascal and Pierre de Fermat, corresponded over two problems from games of chance. Nowadays, probability theory is a well established branch of mathematics that finds applications in every area of scholarly activity from music to physics, and in daily experience from weather prediction to predicting the risks of new medical treatments. This book is written for an introductory probability course taken by social sciences, engineering, and computer science students. The book presents a thorough treatment of probability ideas and techniques necessary for a firm understanding of the subject.