# Policies

| Reference | What it covers |
| [OPA policies](/products/affinidi-trust-fabric/agent-stream/reference/policies/opa-policies.md) | Writing and enforcing Rego policies: the four evaluation layers, the policy editor’s fields, the data a policy evaluates against, and how to test a policy before enforcing it. |

## Pages in this section
- [OPA policies](/products/affinidi-trust-fabric/agent-stream/reference/policies/opa-policies.md): Field reference for the four Rego evaluation layers, the stored policy definition, the input document a policy evaluates against, the pipe-level policy block, and VP evidence.