Signalling via fibroblast growth factors (FGFs) is involved in multiple aspects of vertebrate development. In several instances FGFs act as morphogens, that is secreted signalling molecules that encode positional information in their graded distribution throughout their target tissue. In recent years, work in the zebrafish model system has been instrumental in addressing the cell biological basis of FGF morphogen gradient formation and interpretation. These experiments have benefitted from the optical properties of the zebrafish embryo that render this vertebrate organism particularly suited for advanced microscopic and biophysical approaches.