This skills sheet summarizes the most commonly used Unix commands in the field of bioinformatics. It was created by the e-learning working group of the French Institute of Bioinformatics. The objective is to define the expected Unix skills in bioinformatics. These skills are organized according to increasing levels of difficulty and thematic groups. The skills are cumulative meaning that skills acquired at a given level are required at the next level. Each skill has been defined operationally by following Bloom's taxonomy of learning objectives (Airasian, P. W. et al. A Taxonomy for Learning, Teaching, and Assessing: A Revision of Bloom’s Taxonomy of Educational Objectives. (Longman, New York, NY, USA, 2001)).