Process energy integration and continuous improvement of process technology are everlasting issues to ensure profitability of chemical productions, And both objectives become increasingly important due to long-term environmental effects of energy degradation, such as resource depletion, emissions and the release of ''waste'' heat, The key success factor for process improvement lies in combining up-to-date expertise from different areas in an overall approach. One such approach is the systems engineering concept. It helps to structure and to organize problem-solving processes. We strongly believe that the increasing complexity of large and interlinked chemical production systems and the tightening of global economic pressure force us to use more than ever systematic analysis and design methods to guarantee optimality throughout the entire product life. First we present a brief introduction to systems engineering in general. Then, in the main parr, of the paper, we give examples for optimizing the use of energy in chemical plants in order to illustrate advantages of the systems engineering concept. The examples range from improving the performance of individual pieces of equipment over changes in the process structure up to optimizing process clusters.