In memory of Ingemar Gustavsson 23rd International Colloquium on Animal Cytogenetics and Genomics (23 ICACG) took place in June 9-12, 2018 in Saint-Petersburg, Russia. Organized biennially, the Colloquium runs from 1970. From its very start this meeting is associated with the name of Ingemar Gustavsson to whom we dedicated the Colloquium 2018. The long and productive career of Ingemar Gustavsson had focused on chromosomes and their fundamental role in animal physiology, fertility, health and production in the context of agriculture and veterinary medicine. His meticulous analysis of breeding data performed back in 1964-69 resulted in the unequivocal identification of an association between heterozygosity for the 1/29 translocation in Swedish cattle and reduction in the fertility of the breed. Eventually, the argument in favor of selective elimination of bulls carrying the translocation from the breeding programs prevailed and the field of modern veterinary cytogenetics was established. Participants from fourteen different countries attended the 23 ICACG in Russia, the country having long lasting traditions in cytogenetics and the Scientific schools of N.K. Koltzov, S.S. Chetverikov and A.S. Serebrovsky, geneticists who made important conceptual contributions to studies of chromosomes and genes, population genetics and evolutionary theory as early as in the beginning of the XX-th century. All the abstracts received were subdivided between plenary and seven scientific sessions covering the issues in evolutionary and comparative cytogenetics, cytogenetics and genomes of domestic animals, meiosis studies, particular chromosome analyses, clinical cytogenetics, karyotypes and genomes of vertebrate and invertebrate animals, chromatin studies. In the abstract text below each presentation is marked with a capital letter: "L" stands for lectures, "O" for oral presentations and "P" for poster presentations. We gratefully acknowledge the support from the Saint-Petersburg Association of Scientists and Scholars (SPbSU), Veterinary Genetics Center ZOOGEN, Russian Foundation for Basic Research (RFBR), VEUK, Helicon, Axioma BIO, BioVitrum, Sartorius, DIA-M companies. The current collected abstracts comprise written contributions of the presentations during the 23 ICACG and were edited by Svetlana Galkina and Maria Vishnevskaya. The next Colloquium - 24 ICACG - will be held at the University of Kent in Canterbury (UK) in 2020. Please, cite abstracts as follows: Gall JG (2018) Giant chromosomes and deep sequences: what the amphibian egg tells us about transcription. In: Galkina SA, Vishnevskaya MS, Mikhailova EI (Eds) 23rd Inernational Colloquium on Animal Cytogenetics and Genomics (23rdICACG), June 9-12, 2018, St Petersburg, Russia. Comparative Cytogenetics 12(3): p-p. https://doi.org/10.3897/CompCytogen.v12i3.27748.