This book is the result of many years of teaching introductory statistics within the Psychology Department to undergraduates at the University of Washington. Most of the students have been psychology majors, but there also have been appreciable numbers from other areas such as education, business, nursing, kinesiology, political science, and so forth. This is an introductory textbook, covering both descriptive and inferential statistics. The emphasis is on inferential. At the heart of inferential statistics is the topic of hypothesis testing.