Publication

In the broad sense, publication may mean printing on an office printer for local use; or a full publishing event with press releases, publicity, review copies and so on, in which case a publisher is ideally involved from Phase 1 onwards. If you end up not engaging with a publisher until Phase 4, beware that publishers will probably have their own views on layout and distribution and may therefore show little respect for your thought-out and tested format or market research, however careful your trials were!