This Beckley Foundation Drug Policy Programme briefing paper presents a critical assessment of Plan Colombia. Originally proposed as a peace programme, this soon became a military strategy aimed at weakening the link between illicit drugs and insurgency. The results of this approach in terms of the decline of illegal armies, particularly guerrilla groups, may be considered as a success. In relation to coca cultivation and cocaine trafficking, however, the results show otherwise. This contradiction raises a number of questions about the effectiveness of a predominantly military approach in tackling the drugs problem and the real impact of the supply control strategy on the international market of illicit drugs. The brief explores these and argues that the strategy has failed to address the structural causes of illicit drugs cultivation: poverty, lack of opportunities and on-going conflict. It also discusses how the current emphasis on fumigation has a negative impact on the fragile and strategic eco-system of the Amazonian region, as well as potential health problems for people who live in these areas. Moreover, the brief suggests that a militaristic approach to drug trafficking seems to contribute to the development of what can be called 'markets of violence.' Finally, it is argued that while the power of guerrilla groups - particularly the 40-year-old FARC group that controls some phases of the drug trafficking business - may be in decline, this situation needs to be analysed as part of their lack of political coherence and popular support. A key conclusion from the brief is that the case of Plan Colombia should be used as a learning experience about "what not to do” when addressing complex social and political situations involving the illicit drug trade and internal conflicts in producer countries.