Methods and apparatus, including computer program products, for selecting client adapters. A client abstraction layer identifies one or more selection data elements in a client request and selects an adapter to communicate with the client based on the selection data elements, wherein each selection data element specifies an adapter type, a client type, or data describing the client. The adapter can be selected based on a multi-stage selection process that involves performing an adapter-request process for selecting an adapter based on the selection data elements that specify the adapter type; if the adapter-request process fails to select an adapter, performing a client-identification process for selecting an adapter based on the selection data elements that specify the client type; and if the client-identification process fails to select an adapter, performing a client-description process for selecting an adapter based on the selection data elements that specify data describing the client.