The Mental Functioning Ontology is an ontology for mental functioning, including mental processes such as cognition and traits such as intelligence, and related diseases and disorders. It is developed in the context of the Ontology for General Medical Science and the Basic Formal Ontology. The project is being developed in collaboration between the University of Geneva, Switzerland, and the University at Buffalo, USA. The project is being developed with full involvement of all relevant communities, following best practices laid out by the OBO Foundry. Efforts are currently underway to align with related projects including the Behaviour Ontology, the Cognitive Atlas, the Cognitive Paradigm Ontology and the Neural Electro Magnetic Ontologies.