About the Authors: Marisa S. Bartolomei * E-mail: bartolom@pennmedicine.upenn.edu Affiliation: Epigenetics Institute, Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America ORCID logo http://orcid.org/0000-0001-9410-5222 Rebecca J. Oakey Affiliation: Department of Medical & Molecular Genetics, King’s College London, London, United Kingdom ORCID logo http://orcid.org/0000-0003-2706-8139 Anton Wutz Affiliation: D-BIOL, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Hönggerberg, Zurich, Switzerland ORCID logo http://orcid.org/0000-0002-4377-6330 Citation: Bartolomei MS, Oakey RJ, Wutz A (2020) Genomic imprinting: ...their regulation may differ from genes that are imprinted in the soma. In this collection, Courtney Hannah discusses the function and regulation of imprinted genes in the placenta, with special consideration given to the role of endogenous retroviruses (ERVs) in mediating placental-specific imprinting 8. Because of the unusual nature of imprinting, the identification and study of imprinted genes have driven the adaption and modification of methods and, in some cases, necessitated the development of new technology. Additionally, nuclear transplantation, haploid embryonic stem cells combined with site-directed deletions have more recently shown that the main block to uniparental embryo development is caused by imprinted gene expression.