From the new Cooperative Patent Classification (CPC) system website.
The EPO and USPTO both have highly developed patent classification systems. CPC is an ambitious harmonization effort to bring the best practices from each Office together. In fact, most U.S. patent documents are already classified in ECLA. The conversion from ECLA to CPC at the EPO will ensure IPC compliance and eliminate the need for the EPO to classify U.S. patent documents. At the USPTO, the conversion will provide an up-to date classification system that is internationally compatible.