Since the launch of Industry 4.0 in 2011, its understanding has been driving science and business, and in the case of small and medium-sized enterprises (SMEs), with increasing intensity. That Industry 4.0 is not just a simple transformation and demands immense efforts from companies to implement it, is demonstrated not only by scientific publications, but also by numerous patents/products and editorials in journals. Maturity models (MMs) and readiness models (RMs) for Industry 4.0 are a frequently chosen issue to approach the topic (of implementation). In this paper, based on a structured literature review, 78 models were identified and analyzed, resulting in a set of recommendations for the application of those models by SMEs. Theoretically, this paper contributes to increase knowledge in the area of digitalization, compiling and classifying the different models to support the digital transition. This paper may help practitioners choosing a suitable model for their company, namely SMEs where it is difficult to find solutions.