Psychological prerequisites for comprehension of the instructional material presented by a teacher or contained in a textbook are discussed. Comprehension is regarded as an active cognitive activity at the core of which there is an interplay of cognitive and mnemic processes concerned with establishment of meaningful connections between a new information and an already available knowledge used as a basis for introduction of the new one. Two types of instructional material: theoretical and concrete-practical are charachterized, and conditions for efficient comprehension of them are described (actualization of basic knowledge, optimal relationship between generalizing and specifying elements of the material, introduction of problematicity, etc.).