This book presents the 2019-2020 contests organized by the American Computer Science League. ACSL offers 5 divisions to appeal to the variety of abilities of middle school and high school students. Contests consist of two parts: short problems that cover fundamental concepts in computer science and a programming problem, where students solve a specific problem by writing a computer program in a language of their choice. The fundamental computer science topics covered in the short problem tests include Assembly Language Programming, Bit-String Flicking, Boolean Algebra, Computer Number Systems, Data Structures, Digital Electronics, FSAs and Regular Expressions, Graph Theory, LISP, Prefix/Infix/Postfix Notation, Recursive Functions, and What Does This Program Do? There were four regular season contests, held at each participating school. At the end of the season, the top students were invited to participate in an online all-star competition. This book is organized contest by contest. In each contest, the problems and solutions are organized by division.