The starting point for the onto-semiotic approach was an ontology of mathematical objects that takes into account the triple aspect of mathematics as a socially hared problem-solving activity, a symbolic language and a logically organized conceptual system. Taking the problem-situation as the primitive notion, we de-fined the theoretical concepts of practice, (personal and institutional) object and meaning, with the purpose of making visible and operative, both the mentioned triple character of mathematics and the personal and institutional genesis of mathematical knowledge, as well as their mutual interdependence.