The paper is dedicated to the specification of the structure and the behavior of software libraries. It describes the existing problems of libraries specifications. A brief overview of the research field concerned with formalizing the specification of libraries and library functions is presented. The requirements imposed on the formalism designed are established; the formalism based on these requirements allows specifying all the properties of the libraries needed for automating several classes of problems: detection of defects in the software, migration of applications into a new environment, generation of software documentation. The conclusion defines potential directions for further research.