This paper proposes a new Smart Manufacturing Maturity Model for small and medium-sized Enterprises (SM3E). The SM3E maturity model supports SMEs during the challenging digital transformation journey and paradigm shift towards Smart Manufacturing and Industry 4.0 on three-axis: (i) organizational dimensions, (ii) toolboxes, and (iii) maturity levels. The SM3E maturity model development was based on a literature and critical review as well as interviews conducted during industrial visits. During these visits, SME specific requirements were collected, assessed and taken into account during the development of the SM3E maturity model. Overall, an analysis of maturity levels, based on the working methods and toolboxes of our SM3E maturity model will help SMEs to progress towards Smart Manufacturing and Industry 4.0.