The Biological Weapons Convention (BWC) - officially the Convention on the Prohibition of the Development, Production, and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on Their Destruction - was signed in 1972. Since then, the treaty has evolved into the most important multilateral institution addressing the problem of biological weapons. In many ways the BWC is a classic treaty in which the States Parties are the most important actors. However, with the advancements made in life sciences (such as biology, bio-nanotechnology, and genetics) one would expect the BWC to become increasingly dependent on non-governmental organizations (NGO) such as scientific organizations and industry to remain effective as a multilateral institution. In some cases of multilateral cooperation (for example the International Criminal Court and the Convention on Cluster Munitions) the role of NGO’s has been extensively studied. That is not the case with the BWC. The aim of this theoretically and empirically informed paper is to find out to what extent the role of industry, scientific organizations and other relevant NGO’s in the BWC have changed. To what extent have these NGO’s become agents of contestation, demanding increased access in return for their expertise? We first analyze the extent of NGO involvement in the BWC since its inception. Secondly, by using resource exchange theory, which was developed to explain public-private partnerships, we offer an explanation for the extent to which NGO’s have gained access to the BWC and became agents of contestation. In the last part of the paper we reflect on the consequences of our findings for theorizing the role of NGO’s as agents of contestation in multilateral treaty regimes.