The position of Polish informatics, both in research and teaching, in the world of informatics, has its roots in the achievements of the Polish mathematicians of the Warsaw School and the logicians of the Lvov-Warsaw School. Jan Lukasiewicz is the most famous Polish logician in the world of computer science. Invented by him, the parenthesis-free notation is known as PN (Polish Notation) and RPN (Reverse Polish Notation). Lukasiewicz created multi-valued logic as a separate subject. The idea of multi-valuedness is applied to hardware design (many-valued or fuzzy switching, analogue computer). A many-valued approach to vague notions and commonsense reasoning is the method of expert systems, databases and knowledge-based systems, as well as data and knowledge mining. Stanislaw Jaskowski's system of natural deduction is the basis of systems regarding automatic deduction and theorem proving. He created a system of paraconsistent logic. Such logics are used in AI. Kazimierz Ajdukiewicz, with his categorial grammar, participated in the development of formal grammars, the field significant for programming languages. Andrzej Grzegorczyk has made an important contribution to the development of the theory of recursiveness. Alfred Tarski, and the significance of his work for informatics, is not under consideration in the paper. His achievements are the subject of S. Feferman's article 'Tarski's Influence on Computer Science'.