Models for cell fate specification in developing embryos attempt to create a detailed description of gene regulatory networks typically with a high number of parameters. An alternative approach is to utilize Conrad Waddington's metaphor of flow through a landscape in which valleys represent alternative fates. We will show how this metaphor can be converted into a mathematical description which allows the construction of geometric models offering a parsimonious representation of the data. We will show the application of such geometric models to various different examples.