Claims have been proposed as a means of expressing HCI knowledge that is associated with a specific artifact and usage context. Claims describe design trade-offs and record HCI knowledge related to a specific design, or artifact, as psychological design rationale. Claims are created in the task-artifact cycle of interactive design and evaluation. Usability evaluation establishes a claim for a specific usage context, but this can restrict subsequent reuse of claims-related knowledge. To widen the scope of reuse the knowledge contained within claims and their associated artifacts has to be classified and generalized. To address this problem a schema and method for classifying claims is introduced. The schema elaborates the description of HCI knowledge in claims and enables reuse by describing the assumptions and dependencies upon which a claim rests. Methods for generalising claims and discovering new claims from existing claims and artifacts were investigated. A factoring method for evolving child claims from parent claims and their usage scenarios is described. This employs a walkthrough technique based on Norman's model of action with questions directed at the contributions a claim makes to usability at different stages in interaction. Factoring promotes evolution of child claims that either address different aspects of task support in the same domain as the parent claim, or development of more general child claims for user-interface design. The relationships between claims are represented in maps to illustrate histories of task-artifacts investigation that lead to claims evolution either via the factoring process or by empirical investigation. The schema and method for claims evolution are illustrated by case studies of claims development in tutoring systems and claims for functional requirements for specification reuse support tools. The paper concludes with a discussion of the contribution that reusable claims can make as a repository of HCI knowledge.