A maturity model for micro, small and medium enterprises (MSMEs) is introduced to assess the level of implementation of sustainability strategies and practices in this type of business. According to the literature, only a few sustainability-maturity assessment models intended for MSMEs have integrated the following three factors: environmental knowledge management, environmental strategies and good practices, and environmental management systems. The sustainability maturity model proposed here for MSMEs is capable of supporting the efforts of companies in their attempts to achieve both environmental sustainability and an improvement in their production systems. The model encompasses a four-level qualitative scale and uses supervised classification algorithms to categorize companies through data analysis techniques. After applying the model to a group of MSMEs from different productive sectors in Colombia, the results have shown that 6% of the companies were at an insufficient level, 31% were at an initial level, 45% at a developed sustainability maturity level, and 18% at a consolidated level. This result implies that the decision makers in the latter group have paid greater attention to the strengthening of sustainability progress capabilities and, hence, to the definition of a maturation route.