Megx is a database portal for marine ecological genomics. This field of research is defined as: "the application of genomic sciences to understanding the structure and function of marine ecosystems". Megx.net includes:1) The "Genomes Mapserver": a geographic information system (GIS) to systematically store and analyse marine genomic and metagenomic data in conjunction with contextual information;2) an environmental genome browser with fast search functionalities;3) a database with precomputed analyses (e.g. group-specific genes) for selected complete genomes and4) a tool to classify metagenomic fragments based on oligonucleotide signatures.