JANKÁSEK Marek author KOTYKOVÁ VARADÍNOVÁ Zuzana author ŠŤÁHLAVSKÝ František author text journal article 2021 We present an open (publicly available) and updatable database of the karyotypes of Blattodea which is available at http://web.natur.cuni.cz/zoologie/arthropods/blattodeadatabase/index.html. This database currently contains data on chromosome numbers and sex chromosome systems for 355 (209 cockroaches and 146 termites) cytogenetically and/or geographically distinct populations of 229 species (138 cockroaches and 91 termites). When available, data on chromosome morphology and fundamental number are also included. As this summary of the data on Blattodea cytogenetics follows current taxonomy and phylogeny it enabled us to discuss hypotheses on karyotype evolution. We also point out some cytogenetically interesting phenomena such as extensive karyotype differentiation at low taxonomic levels in some lineages and the change from the X0 sex chromosome system, which is present in cockroaches, to systems with multiple neo-sex chromosomes, present in termites. We encourage the use of modern cytogenetic methods in research on Blattodea cytogenetics to uncover more detailed mechanisms of karyotype evolution in this insect order. We also provide a brief summary of the history of cytogenetic research in Blattodea. Blattodea Isoptera cockroach termite chromosome number karyotype meiosis sex chromosome system online database 10.14411/eje.2021.020 https://www.eje.cz/artkey/eje-202101-0020.php https://www.eje.cz/artkey/eje-202101-0020.php continuing 118 1 192 199 2021 12105759 periodical academic journal