How to annotate a patient's phenotypic profile using PhenoTips and the Human Phenotype Ontology Purpose We have observed that performance of computational search algorithms within and across species improves if a comprehensive list of phenotypic features is recorded. It is helpful if the person annotating thinks of the set of annotations as a query against all known phenotype profiles. Therefore, the set of phenotypes chosen for the annotation must be as specific as possible, and represent the most salient and important observable phenotypes. Towards this end, Monarch has been asked to provide guidance on how to create a quality patient profile using the Human Phenotype Ontology (HPO). Below we detail our annotation guidelines for use in the PhenoTips application, our partner organization.  The guidelines can also be considered more generically so as to be applicable to any annotation effort using HPO or even using other phenotype ontologies.  The annotations should be lim