The book contains a description of natural phenomena and their sequential change in the middle zone of the European part of the former USSR. The author in a popular form acquaints the reader with the phenomena of seasonal life in water bodies (aquatic invertebrates, amphibians and fish) and on land (vegetation, spiders and insects, higher and lower vertebrates), as well as gives methodological instructions for organizing school and circle observations, material for class and circle conversations, seasonal observation program and bibliography on relevant issues. The book is designed for a wide range of readers, teachers of primary (especially rural schools), young naturalists, organizers and leaders of phenological youth circles, young local historians, etc.