A graphics processor operable to render frames that represent a view of a scene using a ray tracing process includes a ray tracing circuit operable to test rays against a ray tracing acceleration data structure for a ray tracing process. The ray tracing circuit comprises a ray testing circuit operable to perform ray intersection tests for nodes of a ray tracing acceleration data structure and storage local to the ray testing circuit for storing data representative of one or more nodes of a ray tracing acceleration data structure for use by the ray testing circuit. Rays for testing by the ray testing circuit are selected from a pool of one or more rays to be tested based on an indication of the ray tracing acceleration data structure node or nodes that have been stored in the local storage of the ray testing circuit.