The lecture presents some of the difficulties associated with the first phase of the project "Creation of German-Czech dictionary of idiomatic minimum", namely the methodology of drawing up an adequate list of German idioms, which can be considered the core of the German idiomatic vocabulary and which can be recommended for advanced students of the German language to master. Discussion focuses on the selection criteria of idioms, existing research, available resources, the issue of corpus research and last but not least the involvement of an online questionnaire to gather data from native speakers.