Invasion of cells through breakdown of the basement membrane is a crucial step during development and cancer metastasis. In this issue of Cell, simple and genetically tractable cellular assay in the worm for elucidating the molecular processes that underlie cell invasion in vivo is described. They demonstrate that the transcription factor Fos is required for cell invasion and identify three of its downstream target genes (encoding a matrix metalloproteinase, hemicentin, and a fat-like protocadherin).