NeXO is a gene ontology inferred directly from large-scale molecular networks. A gene ontology provides structured knowledge about the cellular components, processes, and functions encoded by genes. While most ontologies – including the highly successful Gene Ontology Database (GO) – are constructed through manual expert curation, NeXO is a data-driven gene ontology inferred directly from ‘omics data. NeXO (The Network Extracted Ontology) uses a principled computational approach which integrates evidence from hundreds of thousands of individual gene and protein interactions to construct a complete hierarchy of cellular components and processes. This data-derived ontology aligns with known biological machinery in the GO Database and also uncovers many new structures.