Drawing on sustainability for chemical production processes demands the prior integration of sustainability aspects during process development, when further environmental impacts and production costs become predefined. Micro and milli process technologies provide novel ways for process improvement combined with ecological and economic advantages. This is demonstrated by current developments in this area. In this context, the idea of Novel Process Windows is discussed referring to examples of actual research. A short overview on how to assess sustainability using established tools of evaluation is given as well. This is rounded up with a recent case study of the Kolbe–Schmitt synthesis, performed to disclose the key drivers of further green process development.