Selection of content selection criteria based on entities related by relationship dimensions. In one aspect, a method receives a selection of a seed entity described in entity relation data, the entity relation data defining instances of entities, and for each entity one or more relationship dimensions; generating a set of selected entities; iteratively updating the set of selected entities, each iteration comprising: determining a set of relationship dimensions from the entities in the set of selected entities, each relationship dimension in the set being selected from the one or more relationship dimensions of the entities in the set of selected entities, receiving a selection of one of the relationship dimensions and in response: determining a set of candidate entities from the relationship dimensions and in response to receiving a selection of one or more candidate entities, updating the set of selected entities to include the one or more candidate entities.