This is the fourth ZooKeys special issue containing research presented at a myriapodological congress, i.e. the 18th International Congress of Myriapodology, held from 25 to 31 August 2019 in Budapest, Hungary. The papers are devoted to the two largest groups of Myriapoda: Diplopoda and Chilopoda, and they encompass a wide variety of topics, like faunistics, biogeography, ecology, taxonomy, anatomy and phylogeny.