Pulmonary hypertension (PH) is a life-threatening disease and is characterized by pathological elevation of pulmonary pressure and associated with a heterogeneous spectrum of diseases affecting the pulmonary vasculature (1).The care of patients with PH is a medical specialty in constant flux and shifting paradigms. There are new drugs, changing treatment strategies, renaissance of already almost forgotten surgical techniques like the Potts' shunt and last but not least improved outcome after lung transplantation as last resource for these patients.Despite all available guidelines and recommendations, counselling remains challenging and often has to be patient tailored.Although available treatment options have transformed the outcome of these patients, there is still a long way to go. In this series, we focus on PH in children. While pathobiology and clinical features share similarities in children and adults, pediatric PH provides many differences to adult disease, which need to be considered to provide best possible care for this challenging patient population (Figure 1).The idea for this special series came from a very successful symposium on Pediatric Pulmonary Hypertension which took place in Münster in 2019 organized by Dr. Astrid Lammers in her role as head of the German Working Group of Pediatric Pulmonary Hypertension. Most of the invited speakers, all of them well-known experts in this field, were happy to accept our invitation to write an updated manuscript of their talks. And so, we are now proud to present this special series with the great support of the Editors of CDT.We open with a tribute to Sheila Glennis Haworth, who sadly died in 2020. She actively contributed to our symposium in Münster by giving us the honor presenting the opening lecture on "Lung development and pathogenesis of pulmonary vascular disease". She has been a true pioneer, has participated in the last important decades with more upcoming targeted therapies and she drove clinical and basic research in the field of PH to strive for optimal patient care. Moreover, she has been a passionate medical professional and a true friend to many of us. Therefore, we would like to dedicate this special series to her memory (Appendix 1).The series starts with a commentary from Lammers and Apitz on the new PH definition and its impact on pediatric PH. According to international guidelines, PH used to be defined as elevation of the mean pulmonary arterial pressure (mPAP) ≥25 mmHg. During the 6th World Symposium on PH in 2018, a revised hemodynamic definition of PH was proposed, lowering the threshold from ≥25 mmHg to >20 mmHg (2). This new definition has also been accepted by the Pediatric Task Force of the World Symposium to establish a uniform language and facilitate transition to adult services (3). This decision resulted in controversial debates within the expert community as the new definition may lead to overdiagnosis and overtreatment of PH. Therefore, a critical expert discussion on the impact of the new PH definition in pediatric PH is p...