GATS covers all public measures, instruments and rules that "affect trade in services". It covers all service sectors and all ways of offering services, whether through the sale of services in another country, by consumers purchasing services in other countries, by investing in other countries or by people taking up work and providing services in a another country.
A country that opens up a service area for foreign competition gives foreign companies free access to sell these services domestically, to establish companies that offer these services, to bring with them the staff the company deems necessary – if no reservations are made for some of this when the country decides to open a service area for foreign competition.
No country can withdraw commitments given – unless one offers to open other service areas of the same value to other WTO countries for competition from abroad. This is what makes GATS as dramatic as an international agreement.