The HPO is copyrighted to protect the integrity of the vocabularies, which means that changes to the HPO vocabularies need to be done by HPO developers. However, anyone can download the HPO and use the ontologies or or other HPO files without license for any purpose under three conditions:

1. That the Human Phenotype Ontology Consortium is acknowledged.
2. That any HPO Consortium file(s) displayed publicly include the date(s) and/or version number(s) of the relevant HPO file(s).
3. That neither the content of the HPO file(s) nor the logical relationships embedded within the HPO file(s) be altered in any way.

We suggest that you follow standard scientific citation practice if you use the HPO in publications, but we will not contact our lawyers if you do not. The HPO vocabularies and annotations are available to all public and private sector users, with no licensing requirements.