this book appeared in 1968. It is an excellent book and in the 2nd edition it has been updated to bring the coverage closer to the way topics are treated in research; in particular, it covers now convergence in D[0, infinity), necessary to deal with convergence of stochastic processes. It is more elementary than Jacod and Shiryaev's Limit Theorems for Stochastic Processes, a book that deals with much more advanced topics and applications to start with and Billingsley's is therefore more readable making it excellent to introduce advanced students to the subject. Billingsley provides a good collection of examples that increase the readability of the textbook and makes it easier for students to appreciate several of the technicalities. It is not an "easy" book and students must be willing to put a lot of hours and efforts into understanding the topics, but it is a rewarding book.[size=1.5]It is the book that "popularized" this area of probability and still remains quite usef