Learning a language opens up new horizons, whether it´s for your international business dealings, a way to access other cultures or enhance your social life, or simply a hobby for your own enjoyment. Of the courses on offer outside of formal education, the ones offering language skills are among those most in demand. There are a huge number of different types of provider on the market; the differences in the quality of their services are just as great. Quality standards are necessary to provide a positive and successful learning experience, and also to make sure that the cost of learning a language, which can often be considerable, is worth it. The most important requirements language service providers have to meet are given in the International Standard ISO 29991. This bilingual (German/English) publication gives an overview of the content of the standard and offers guidance for those wishing to compare what´s on the market.