This manual for authors of lessons to be used with the PLATO interactive computer system provides an overview of the system, describes its characteristics, and provides detailed instructions for the use of system features to author a lesson. An introductory chapter describes sign on procedures and various online features available to the author, including the online reference manual, system announcements, catalog of available lessons, personal notes, and interactive communication. The remaining chapters focus on the TUTOR programming language, the elements of a PLATO lesson, and the creation of displays; how to use the TUTOR editor; features that provide immediate feedback to the student and control branching; the storage of individual student records and using these "variables" to provide individualized feedback; writing conditional statements and iterative statements using TUTOR commands and information in student variables; additional capabilities for judging student responses; and special branching capabilities. Exercises are provided at the end of each chapter. (CHC)