Most of the literature published to date focuses on issues of collusion between blockchain participants (see Chapter 8). However, there is much less discussion regarding how companies that operate in the “real space” could use blockchains to facilitate the creation and operation of illegal agreements. Against this background, the current chapter starts by exploring the different forms that such collusion could take. I first consider the impact of smart contracts, and the specific issues they entail (Section 1). The next section analyzes the stability of such agreements. It notably highlights factors that influence this stability (Section 2). I conclude by explaining how these can and should be detected and prosecuted (Section 3).