A method of evaluating an attribute-based access control policy, ABAC policy, for an access request, wherein: the method is implemented at a processing means communicatively connected to a nearby attribute value source and at least one remote attribute value source (S1, S2), the nearby attribute value source differing from the remote attribute value source(s) by having relatively lower network distance or response time or round-trip time with respect to the processing means; and the access request contains one or more explicit attribute values, which together with the ABAC policy define at least one implicit reference to a further attribute value, which is retrievable from one of said attribute value sources, the method comprising the steps of: reducing the ABAC policy at least by substituting said one or more explicit attribute values for corresponding attributes appearing in the policy and by substituting further attribute values, to which the access request and the policy make implicit reference and which are retrievable from the nearby attribute value source; caching references to further attributes to which the access request and the simplified policy make implicit reference and which are retrievable from a remote attribute value source (S1, S2) only; after completion of said reducing, caching the policy as a simplified policy; retrieving attribute values, as specified by the cached references, by one call to each concerned remote attribute value source(s) (S1, S2); and evaluating the cached simplified policy for the access request by substituting the retrieved attribute values. the method is implemented at a processing means communicatively connected to a nearby attribute value source and at least one remote attribute value source (S1, S2), the nearby attribute value source differing from the remote attribute value source(s) by having relatively lower network distance or response time or round-trip time with respect to the processing means; and the access request contains one or more explicit attribute values, which together with the ABAC policy define at least one implicit reference to a further attribute value, which is retrievable from one of said attribute value sources, the method comprising the steps of: reducing the ABAC policy at least by substituting said one or more explicit attribute values for corresponding attributes appearing in the policy and by substituting further attribute values, to which the access request and the policy make implicit reference and which are retrievable from the nearby attribute value source; caching references to further attributes to which the access request and the simplified policy make implicit reference and which are retrievable from a remote attribute value source (S1, S2) only; after completion of said reducing, caching the policy as a simplified policy; retrieving attribute values, as specified by the cached references, by one call to each concerned remote attribute value source(s) (S1, S2); and evaluating the cached simplified policy for the access request by substituting the retrieved attribute values. reducing the ABAC policy at least by substituting said one or more explicit attribute values for corresponding attributes appearing in the policy and by substituting further attribute values, to which the access request and the policy make implicit reference and which are retrievable from the nearby attribute value source; caching references to further attributes to which the access request and the simplified policy make implicit reference and which are retrievable from a remote attribute value source (S1, S2) only; after completion of said reducing, caching the policy as a simplified policy; retrieving attribute values, as specified by the cached references, by one call to each concerned remote attribute value source(s) (S1, S2); and evaluating the cached simplified policy for the access request by substituting the retrieved attribute values.