This paper is an attempt to show what parameters come into play when dealing with the problem of difficulty in foreign language learning. After subjecting the hierarchy of difficulty set up by R.P. Stockwell and J.D. Bowen to a critical examination, the author discusses various parameters such as individual and national difficulties, the chronological factor and its effects on interstructural and intrastructural interference, and the type of learner concerned. He comes to the conclusion that the setting up of scales of difficulty requires the cooperation of linguists as well as of pedagogues, psychologists, and representatives of other disciplines. (Author)