The search division classifies a patent application under the provisions of the CPC as well as the IPC. In practice, classification is first performed in the CPC, and the relevant IPC symbols are then generated from the CPC allocations by one-to-one concordance (see the CPC to IPC Concordance List (CICL), published on the CPC website).

The CPC classification allocated is as precise and comprehensive as the classification system permits. The CPC comprises "invention information" symbols and "additional information" symbols. Additional information symbols encompass the use of CPC indexing codes. Where it is necessary to assign more than one CPC classification symbol for the invention itself, the symbol which, in the search division's opinion, most adequately identifies the invention, or, when this presents difficulties, the symbol which identifies the invention for which most information is given, is indicated first.

As with the IPC, CPC classification preferably takes place when the search division has studied the content of the application in order to carry out the search.

As for the IPC classification, the CPC classification is determined without taking into consideration the possible future content of the application after any amendment, since the classification relates to the disclosure of the published application, i.e. the application as filed.

However, if the search division's understanding of the invention, or of the content of the application as filed, alters significantly as a result of the search, the search division amends the CPC classification accordingly, making use of the appropriate classification tools. Unlike changes to the IPC classification (see B‑V, 3, above), this amendment can be made even after the preparations for publication have been completed.

When the scope of the invention is not clear (e.g. a partial search is necessary), or in the case of lack of unity of invention, the principles described in B‑V, 3.2 and 3.3, for the IPC classification apply equally to the CPC classification.