DDI Profiles are formal, machine-actionable XML documents that specify additional constraints on the content of a DDI XML document, over and above those specified by the document's associated XSD schema. These DDI profiles are intended to be used in the context of validating DDI2.5 and DDI1.2.2 documents that are being submitted to CESSDA Data Catalogue from participating Service Providers. Firstly, the Profiles provide human-readable guidance for metadata professionals e.g. whether an element is optional, recommended or mandatory. Secondly, they support machine-actionable validation by the CESSDA Metadata Validator, an online and command-line based set of tools, whose primary goal is to improve metadata quality so that resulting aggregations of such metadata in the CESSDA Data Catalogue have improved utility for the research community.