Overt collusion involves an illegal explicit agreement whereby firms cooperate with one another, whereas tacit collusion is an informal agreement with no succinct communication or cooperation regarding actions. Though the firms raise their own surplus by colluding; from a welfare perspective, collusion is inefficient. The monopoly outcome reduces total economic surplus via deadweight loss incurred by higher prices and lower output than what is socially the optimum. Both cooperative and non-cooperative collusion yield this outcome, and so competition authorities wish to deter both forms. This essay will explore the settings in which non-cooperative collusion operates most effectively, which will lead to an understanding of why competition authorities find difficulty in detecting it, let alone deterring it.