Maturity models (MMs) are tools to assess how reliable is an organization and to identify its strengths and weaknesses. The increasing number of MMs developed for several domains or specific contexts based on different architectural styles (AS’s), makes more difficult its understanding and reuse. This paper aims to identify and compare the AS’s of organizational MMs for different domains. A Systematic Literature Review (SLR) was conducted. The SLR included 70 studies that describe the architecture of MMs for different contexts. A classification scheme was defined and tested with a group of MMs. Another group of MMs adopted the AS of existing models. As a result, the MMs found were classified into nine AS’s. The AS’s derived from SW-CMM and CMMIstaged are quite similar. The ISO-SPICE-based and the OPM3-based architectures are the most different. The AS’s most used in studies were the CMMIbased and the progression-staged model.