The last twenty years have seen major advances in our understanding of animal development. Genes regulating particular processes have been identified and, in many instances, they have been linked to human diseases, but how genetic information is transformed into three-dimensional tissues and organs remains an open question. We are seeking to fill this critical gap in knowledge by exploiting mouse genetics, high resolution quantitative imaging and gene expression profiling to investigate mechanisms of cell lineage specification, tissue patterning and morphogenesis, using the mouse as a model system. I will provide an overview of our interests and discuss some of our studies. My talk will reflect our focus on two distinct but interrelated events; blastocyst development and gastrulation.