The proposed textbook is the first part of the course of elementary geometry by authors L. S. Atanasyan, N. S. Denisova, E. V. Silaev. It is intended for students of mathematical and physical-mathematical faculties of pedagogical universities and institutes when they study a course of elementary mathematics and undergo a workshop on solving problems. It can also be used by teachers and students of schools and classes with in-depth study of mathematics. The presentation of the theory is accompanied by a large number of tasks that correspond to the theoretical content of each chapter.