Contextual targeting

Contextual targeting is choosing where to show an ad based on the content around the slot, such as the page topic, keywords, video genre or app category, rather than on data about the viewer.

Context needs a shared vocabulary. The IAB Tech Lab's Content Taxonomy 3.1 has 704 categories in up to four tiers, under 37 top-level headings, by our count of the published file (IAB Tech Lab, Taxonomies repository, accessed 9 November 2026). In OpenRTB 2.6, sellers put category IDs in fields such as site.cat and content.cat, and cattax names the taxonomy. Value 9 for Content Taxonomy 3.1 was added in release 2.6-202501 on 27 January 2025, alongside genres and gtax for CTV programmes.

Contextual targeting does not rely on cookies or cross-site IDs, which makes it attractive where consent is hard to obtain. It is not free of privacy rules, because bid requests still carry device data. Its quality depends on the classifier: a seller, a verification vendor or the buyer's own model may label the same page differently.

Example: A running-shoe brand targets pages with "cat": ["227"] and "cattax": 9, which is "Running and Jogging" in Content Taxonomy 3.1. It reaches readers of race reports and training plans without using any data about who they are.

Related terms: brand safety, third-party data, curation, CTV, Topics API, AdCOM.

Authoritative source: IAB Tech Lab, Content Taxonomy 3.1 (Taxonomies repository on GitHub, accessed 9 November 2026).