Windows of opportunity for changing drug laws open infrequently and they often close without legislative change being affected. In this paper the author, who has been intimately involved in the process, describes how evidence-based recommendations to ‘decriminalize’ cannabis have recently been progressed through public debate and the political process to become law in Western Australia (WA). The Cannabis Control Bill 2003 passed the WA Parliament on 23 September. The Bill, the legislative backing behind the Cannabis Infringement Notice (CIN) Scheme, came into effect on 22 March 2004. This made WA the fourth Australian jurisdiction, after South Australia, the Australian Capital Territory and the Northern Territory, to adopt a prohibition with civil penalties scheme for minor cannabis offences. This paper describes some of the background to the scheme, the process by which it has become law, the main provisions of the scheme and its evaluation. It includes reflections on the role of politics and the press in the process. The process of implementation and evaluation are outlined by the author, foreshadowing an ongoing opportunity to understand the impact of the change in legislation