The ISCO provides a systematic classification structure which encompasses all occupations of the economically active population. The ISCO was used to classify vacancies. The classification structure consists of four levels: major groups, sub-major groups, minor groups, and unit groups. There are ten major groups. The ten major groups of the ISCO classification are:

  1. Legislators, senior officials and managers;
  2. Professionals;
  3. Technicians and associate professionals;
  4. Clerks;
  5. Service workers, shop and market sales workers;
  6. Skilled agricultural and fishery workers;
  7. Craft and related trade workers;
  8. Plant and machine operators and assemblers;
  9. Elementary occupations;
  10. Armed forces.