The aims of the 2021 European Training Requirements (ETR) in Paediatric Endocrinology and Diabetes (PED) are to (1) provide standards to harmonize training programmes in PED between different European countries, (2) establish clearly defined standards of knowledge and skills required to practice PED at the tertiary care level, (3) foster the development of a network of competent tertiary care centres for PED in Europe and globally, and (4) improve the quality of care for children and adolescents requiring PED services. This ETR in PED specifies the requirements for training institutions, trainers, and trainees. It also provides the detailed syllabus/core content that trainees are expected to achieve in order to become competent independent clinicians in PED. References to consensus guidelines produced and/or endorsed by ESPE are included. The target users are trainees in PED, trainers, and all involved with quality assurance and accreditation. The process to develop and approve this 2021 ETR has been rigorous and involved trainees and consultants in paediatric and adult Endocrinology, ESPE (Syllabus Task Force, Education and Training Committee, Council), European Academy of Paediatrics (Tertiary Care Council, Assembly), European Board of Paediatrics, and Union of European Medical Specialists. Implementing the ETR will complement professional regulatory requirements for postgraduate training in PED in different countries and allow harmonizing standards across Europe. ETR is publicly available at www.eurospe.org/education/education-training-syllabus and at https://www.uems.eu/__data/assets/pdf_file/0007/133990/UEMS-2021.17-European-Training-Requirement-in-Paediatric-Endocrinology.pdf.