Immature teeth should be kept alive if at all possible. If this is not possible and regenerative endodontic therapy is not possible, these teeth require root canal treatment. The endodontic treatment of immature, devitalized teeth differs from that of mature teeth in a number of important respects. A summary of the most important working steps is described in this course. Particular attention is paid to root canal irrigation and temporary and permanent root fillings. It will be shown how even previously hopeless cases can be treated thanks to new materials and techniques.