J. Mark Cock obtained his PhD from Leeds University in 1985 and worked during his early career on several aspects of terrestrial plant biology including nitrogen metabolism, nodulation and self-incompatibility. In 2002, Mark Cock moved to the Station Biologique de Roscoff (France) where he initiated a project aimed at developing the filamentous brown alga Ectocarpus siliculosus as a genetic model species for the phaeophyceae. This project included the sequencing and analysis of the 214 Mbp Ectocarpus genome, work that was carried out in collaboration with Genoscope and the VIB in Ghent and involved the coordination of a large international consortium. The brown algae are one of only a small number of eukaryotic groups to have evolved complex multicellularity and current work is aimed at understanding how developmental complexity evolved in this group with a particular focus on two key developmental processes, life cycle regulation and sex determination. Genetic and genomic approaches are being applied to identify key regulators of these processes and to dissect regulatory pathways. Major recent advances include the cloning of the first brown algal developmental genes by forward genetics, the identification of master regulators of the Ectocarpus life cycle and description of brown algal sex chromosomes and sex-determination genes.