Abstract: The paper aims at characterizing the problem of patent ambushes and deriving policy proposals on how this problem should be tackled. To reach this aim, the paper is structured into four sections. The first two sections provide a brief overview of the basic rationale for a patent system and the incentives of IPR holders to make innovations available to other users. The third section introduces into the topic of submerged patents and especially assesses how this can give rise to patent ambushes. The fourth section first discusses the applicability of EU competition laws to tackle the problem of patent ambushes. The important finding that these laws do not appear to provide an effective safeguard against patent ambushes subsequently leads to an assessment of the question how the risk can be mitigated via the adoption of appropriate IP rules by standard-setting organizations. A checklist is developed which allows an assessment of IP rules with respect to their capability of mitigating the risk of patent ambushes.