Lung cancer is the third most frequent new cancer diagnosis in Germany. An elaborate clinical diagnosis is essential for successful therapy planning. The necessary examinations are defined in the current S3 guideline on lung cancer diagnosis and therapy. A compilation of diagnostic reports has led to the current 7th edition of the TNM system. According to this update staging is carried out in terms of tumor extent, lymph node status and distant metastases. The resultant tumor stage forms the basis for individual therapy planning. Current guidelines as well as the current TNM system are presented. The usefulness of modern cross-sectional imaging and the possible modalities in this system is reported.