Cooperation among players is often a good deed to pursue. The famous "Prisoner’s Dilemma" in game theory has long been an example of showing how non-cooperation results because of conflict of interest among agents. My thesis investigates how factors like imperfect public monitoring, emergence of an external threat influences the cooperative behaviors among players in dynamic environments. Chapter 1 investigates bidder collusion in repeated procurement auctions without communication or side payments, focusing on the case of bidders having identical costs under imperfect public monitoring where only winners, not bids, are publicly observed. It presents a simple bid rotation scheme, in which bidders take turns entering bids equal to the auctio...