Ensembl (www.ensembl.org) is an open access resource integrating genome, variation, comparative genomics and regulation data for over 100 vertebrate species including 16 mouse strains. These sessions are an introduction to the Ensembl genome browser and its mouse genomics resources as part of the '3rd Programmable nucleases (CRISPR/Cas9) – Transgenesis Course' in Prague, 16th – 20th April 2018.