Adapting David Beetham's Legitimation of Power model (1991) for social sciences, and taking into account syntetic theories of the policy process and recent developments in policy change theories and literature (Howlett, 2007; Howlett & Cashore, 2009; Mcbeth, Shahanan, Arnell, & Hathaway, 2007; Real-Dato, 2009a, 2009b; Stewart, 2006; Wilson, 2000, 2006), this paper explores and defines an approach for the study of policy stability and change called "legitimation and policy dynamics" (LDP approach or model). As an analitical device, the "legitimacy pattern" secures stability and a logic of incremental change. Dramatic events like shocks (as well as internal dynamics) may promote major policy change, whose origin is located with the emergence and identification of non legitimate power forms into the policy regime: a) "policy or law inconformity"; b) discrepancy with shared beliefs" c) consent withdrawal and/or d) the inefficacy in policy performance (outcomes and impacts).