Preface of the special issue on Branching Processes and Applications (IWBPA2021)

The 5th International Workshop on Branching Processes and their Applications (IWBPA2021) was held on 6th, 8th, 13th, 15th, 20th and 22nd April 2021. It was the last in a series of meetings held every three years in Badajoz (Spain). Due to the COVID-19 pandemic, the IWBPA2021 took place virtually using video conferencing tools. The 2021 year’s conference continued the tradition of the previous meetings in facilitating the exchange of research ideas in this field and related processes. The IWBPA2021 meeting was the fifth in the series of IWBPAs promoted and organized since 2009 by the research group Branching Processes and their Applications at the Department of Mathematics of the University of Extremadura, Spain, and scientifically sponsored by the Spanish Society for Statistics and Operations Research (Sociedad de Estad ıstica e Investigaci on Operativa) and the Institute of Advanced Scientific Computation of Extremadura (Instituto de Computaci on Cient ıfica Avanzada de Extremadura). There were 145 participants and 58 speakers from 22 countries who contributed to the success of the workshop. The presentations at the workshop maintained a healthy balance between the theoretical and practical aspects of branching processes. The speakers articulated the fact that this research area is very active and produces interesting results. The conference program and talks are available on the website (https://sites.google.com/view/iwbpa21-branching-unex). The Proceedings consist of 15 selected papers whose topics have been classified into the following parts: