The ‘Genes and Development’ workshop focused on recentadvances in our understanding of the molecular control ofplacental development, focusing on the mouse model. JayCross gave an introduction to mouse placental developmentthat outlined the major structures and cell types. He alsoreviewed the considerable progress that has been made indefining molecular pathways controlling development usingmutant and transgenic mice as well as increasing knowledge ofthe biology underlying implantation and establishment of themature placenta [1,2]. One of the important general findings toemerge in recent years is that development and function of thedifferent sub-structures of the placenta can be interdependentand able to adapt to defects in other parts. This can complicatethe analysis of a phenotype in that some types of changes cansimply represent secondary changes reflecting attempts tocompensate, and investigators need to take this into consider-ation before making conclusions. The remaining speakers wereselected to discuss different aspects of placental developmentand highlight the use of new experimental approaches forstudying mouse placental development and function.