Fate-mapping and lineage-tracing studies that were performed on mouse embryos maintained in culture have provided a unique insight into the morphogenetic processes that take place during gastrulation and early organogenesis. These experiments allow the analysis of the developmental fate and the differentiation potency of cells that are allocated to different tissue lineages during postimplantation development. Results of lineage analyses using in situ labeling and cell transplantation have led to the construction of maps that describe the regionalization of cell fate in the embryonic germ layers and their derivatives at various stages of mouse development. From this spatial description of where cells of a particular lineage are localized at successive developmental stages, it is possible to track the most likely pattern of morphogenetic movement of cell populations in the normal and mutant mouse embryos during gastrulation and organogenesis.