This book is designed to introduce the reader to some fundamental ideas about probability. The mathematical theory of probability plays an increasingly important role in science, government, industry, business, and economics. An understanding of the basic concepts of probability is essential for the study of statistical methods that are widely used in the behavioral and social, as well as the biological and physical, sciences. The material in this book is written for students at approximately the seventh or eighth grade level. It is presumed that the student has an adequate background in arithmetic. No previous experience in probability is assumed. Parts of the text are in programmed form. Each chapter includes problems and exercises. Chapters include: (1) Introduction; (2) Finding Probabilities; (3) Counting Outcomes; (4) Estimating Probabilities; (5) The Probability of A or B; (6) The Probability of A and B; and (7) Conditional Probability. Discussion of problems and exercises are at the end of the text. (RH)