Title: Stable and Unstable Operations in mod p Cohomology Theories Authors: Andrew Stacey and Sarah Whitehouse Author's e-mail address: a.e.stacey@sheffield.ac.uk s.whitehouse@sheffield.ac.uk AMS classification number: 55S25, 55P47 Other useful information: math.AT/0605471 Abstract: We consider operations between two multiplicative, complex orientable cohomology theories. Under suitable hypotheses, we construct a map from unstable to stable operations, left-inverse to the usual map from stable to unstable operations. In the main example, where the target theory is one of the Morava K-theories, this provides a simple and explicit description of a splitting arising from the Bousfield-Kuhn functor. This is an updated version of an earlier submission. The proof of proposition 3.2 has been corrected; other minor improvements have been made.