This article focuses on the development of antitrust policy in transition economies in the context of preventing explicit and tacit collusion. The experience of BRIC countries, Kazakhstan, Ukraine and the CEE countries () in creating antitrust institutions was analyzed, including both legislative and enforcement practices. This article analyzes enforcement issues, in particularly: classification problems (tacit vs explicit collusion, vertical vs horizontal agreements), flexibility of prohibitions ("per se" vs "rule of reason"), design of sanctions, private enforcement challenge, leniency program mechanisms, the role of antitrust authorities etc. The main challenges for policy effectiveness in this field were outlined. JEL Classification: K21, L41, L42.