The protracted nature of the Colombian conflict has allowed the emergence of numerous attempts for its resolution (intense military offensives and different models of negotiation). Regarding the attempts of negotiation, some of them have resulted in durable peace agreements while others have failed during the process. For example, in 1991, the government negotiated the reincorporation into the political life of the guerrillas M-19 and EPL, and recently in 2002-2007, the government held a peace process with the AUC paramilitary group, which produced the demobilization of approximately 40.000 rebels. However, the scenery of resolution with two remaining guerrillas (FARC and ELN) is different, after more than 26 years of failed negotiations and tough military offensives; it has not been possible to settle the conflict with them. What explains the different results in the peace processes with the armed groups? I suggest that in order to identify opportunities for negotiations and more effective peace processes, states and third parties, should regard more seriously the character of the different armed groups (motivation, leadership, strategies, social composition, organizational structure, etc). Therefore, by doing a comparative analysis of the AUC and FARC peace processes. I found out that: 1. the type of violence and financial sources are not determinant factors to reach a negotiated settlement with rebel groups. It is false that is more difficult to negotiate with armed groups pursuing high benefits from war, at least not in Colombia. 2. That the degree of task cohesion, the group cohesiveness, and social support are extremely relevant to the state engage and manage possible crisis and setbacks during the negotiations. Armed groups are different and those differences have positive and negative impacts when negotiating with them.