As the backbone of modern industry, especially for developing countries such as China, the steel and iron industry has been a double-edged sword for the great economic benefits it brings on one side, and the pollution it causes on the other side. Moreover, rising energy prices have left iron and steel enterprises no choice but to improve energy efficiency as well as make the most effective use of waste energy as secondary energy sources. This dissertation explores the potential for Energy Efficiency (EE) improvement through Industrial Symbiosis (IS) for the iron and steel industry based on the study of existing available practices and the status of energy management in Chinese iron and steel enterprises. This PhD seeks to integrate, extend and link knowledge on areas of IS and EE by answering the following primary research question: How can energy-intensive industries improve EE through IS? In order to answer this question, six leading iron and steel enterprises from Mainland China and Taiwan were selected as case studies. Based on data collection followed by both individual case analyses and cross case analyses, the energy efficiency improvement approaches discovered in this research for energy intensive industries, especially the iron and steel industry, have been identified as core finding of this research. Specifically, the following five main perspectives can be considered for further discussion:

• Establishment of an Energy Management Systems (EnMS) for the iron and steel industry It is vital to establish an EnMS which meets the specific needs of the firm with consideration of four main factors: (1) company ownership, (2) responsibility distribution in the EnMS, (3) the energy saving project management approach and (4) evaluation of energy management projects.
• Identification of Energy Efficiency Balance for the iron and steel industry It is important to keep an appropriate balance in technological development and managerial improvements to ensure energy efficiency improvement.
• Establishment of an Energy Symbiosis Model for the iron and steel industry Four types of energy symbiosis have been identified, which provides potential options for making the most of the recovered waste energy.
• Establishment of a Geographical Proximity Model Geographical Proximity has been identified as the major barrier in inter-firm level energy symbiosis network construction. This model also shows the mechanism of energy symbiosis establishment.
• Establishment of an Energy Management Maturity Model (EMMM) for the iron and steel industry As a practical tool, an EMMM provides potential directions for well-balanced energy efficiency improvements from the perspectives of both technological development and managerial improvement at four IS levels.

Overall, this study seeks to contribute to the body of knowledge in the field of IS and EE in the following ways: (1) Clarify the boundary of IS and the bottleneck on conducting energy symbiosis; (2) enrich the connection of IS from the energy symbiosis point of view; (3) reveal the dominant bottleneck of promotion of Energy Symbiosis; (4) identify the balance of EE improvement; (5) link IS with EE to enrich understandings of the application of IS. The major practical contributions are that energy-intensive industries, especially the iron and steel industry, can benefit from an EMMM, which provides an overview of existing energy usage and potential direction for EE improvement. This research also provides a theoretical basis for EIP (Eco-Industrial Park) planning and construction for decision makers.