The effectiveness and safety of induction and maintenance therapy of Ustekinumab and other biologics will be assessed in different relevant subgroups of Crohn`s Disease patients. To this end, different confounders have to be considered. Patients followed-up for several years will likely receive changing treatments. These changes have to be taken into account. Furthermore, the decision to prescribe, to stop or to continue a treatment depends on the availability of treatment options and experiences with these alternatives: