This article does not deal with patent databases, retrieval systems or hardware and software facilities available to search engineers. Rather, the different types of patent searches required in an industrial company are discussed. In order to supply this retrospective patent information so as to satisfy the needs of the company, effective communication between the patent engineers and search engineers is required. The basis for such effective communication is familiarity with the possibilities and difficulties of patent and search work, which is obtained by training and co-operation. Together with improved access to patent documents such co-operation, in which outsourcing also plays a role, will tend to enhance the significance of retrospective patent searching.