With the EU Clinical Trial Regulation becoming effective on 31 January 2022, a new era of clinical trials with medicinal products has begun in the EU/EEA. The EU legislator provided for a 3-year transition period in which the former system under the EU Clinical Trials Directive and the new system under the EU Clinical Trial Regulation are available in parallel.  Sponsors need to know how to best use this period for ongoing clinical trials, but maybe also for trials that are soon to be submitted. Strategic decisions will be necessary and the switch from one legal framework to the other must be well understood.