Background: Smoking is significant global public health problem and legislation is often used to control it. Many countries have laws banning smoking in public places and some have banned smoking in vehicles carrying children. Not all such legislation has been effective. To assist policy makers guidance is needed on whether such legislation would be acceptable to the public or even work. Objectives: Review the effects of legislation as a tool in tobacco control using the example of bans on smoking in vehicles carrying children. Methods: Realist review method was used as no RCTs and few evaluations exist in this area. Initial programme theory and important potential threats to legislation and candidate middle range theories that might explain these threats were developed. Searching and pearling, initially identified 65 studies relevant studies. As new avenues for enquiry emerged, additional studies were sought. Results: Our results will focus on the additional insights a realist review can bring. For example, despite the absence of RCTs and the limited number of evaluations on the effects of such legislation, the realist review method enabled us to identify a structurally coherent framework (or programme theory) that explained and increased understanding of the ‘threats’ that a piece of legislation faces from conception to enforcement. The method allowed us to identify the underlying mechanisms that appear to operate to threaten public health legislation and also the contextual influences that caused these mechanisms to operate. Our initial findings indicate that these threats may well be transferable across other legislative domains. Discussion and Conclusion: This review is in progress and will be completed in September 2010. Our review indicates that despite the ‘paucity’ of evidence in this field, sense can be made of when it is that public health legislation may be appropriate and likely to succeed.