The improvement of industrial engineering performance is currently a key issue. Companies can achieve such an improvement in different ways. One way, especially for companies operating in a multi-project environment, is a successfully operating Project Management Office (PMO). Recent studies have revealed that a successful PMO is a key factor influencing organisational performance. The author of this study conducted a world-wide research with a sample of over four hundred PMO cases to identify what determines the success of their operations. This study revealed that to achieve a successfully operating PMO, we should focus on the activities of the PMO during two periods: short term (up to one year) and long term (two or more years). Consequently, in each of these time frames, there are different issues that need to be addressed to run a successful PMO and, thus, improve industrial engineering performance. Moreover, the efficacy of operations in a multi-project environment is crucial for practitioners. Therefore, the findings of this research will help managers to improve organisational performance, which should result in the ability to manage more projects on time and within the budget and scope of the PMO. This paper advances the current state of knowledge on PMO success factors and explores new research areas.