Eco-efficiency improvements in manufacturing is a controversial subject for researchers, practitioners as well as policy makers. The widely accepted definition of "doing more with less" is not accurate enough to guide the design of improvements that can deliver products in a sustainable way. The outcome of these challenges is evident through significant environmental performance variations across various levels of manufacturing operations. The study is driven by the complexity of manufacturing systems and sought to offer design support for practitioners that aim to improve eco-efficiency. A maturity model has been developed in this work that simulates the influence of manufacturing practices on eco-efficiency. The model takes the form of a maturity grid (PMGE) that overlooks practices at process, management systems and top-management levels and incorporates 15 dimensions of performance overall. Evidence shows that practices tend to evolve from reactive to proactive as manufacturing systems mature and embrace eco- efficiency as a systemic property. It was also found that mature companies achieve improvements in energy and resources by relying on existing internal capabilities. Tools to facilitate research and intervene with practitioners in real-life problems were developed and tested. The researcher combined research findings and tools into a maturity-based method (PMGEM) for eco-efficiency improvements. The method intends to help practitioners plan and design eco- efficiency improvements aligned to existing internal capabilities and adopt a more proactive behaviour to environmental challenges. PMGEM was ultimately applied in two case studies with ultimate goal to help practitioners resolve real-life challenges. The applications were positively commented and encourage further work in this field. The researcher envisages that methods such as PMGEM are deeply needed in manufacturing to support practitioners approach complex concepts such as eco-efficiency. Simplification and decomposition techniques with a clear intended use can facilitate the implementation of ambitious improvement strategies for sustainable development.