Over the past two years the United Nations Industrial Development Organization (UNIDO) assessed 50 parks in eight developing and transition countries against 51 prerequisites and performance indicators outlined in the International Framework for Eco-Industrial Parks (International EIP Framework). The eight countries covered are: Colombia, Egypt, Indonesia, Nigeria, Peru, South Africa, Ukraine, and Viet Nam. This article provides a summary of the analysis and lessons learned from the assessments of the industrial parks and their performance against the International EIP Framework. The methodology is based on assessments of the current and intended performance of the industrial parks on four key categories (park management, environmental, social, and economic), supported by a scoring method. The analysis indicates that the International EIP Framework can be regarded as a practical and relevant means to assess the performance of industrial parks, as well as a basis to identify and prioritize EIP initiatives to strengthen their performance. There is a wide range of performance among the industrial parks assessed. Higher average current performance against the International Framework can be found in Colombia (68%), Indonesia (67%), and Viet Nam (63%). Ukraine and South Africa have the highest improvement potential (27% and 25%, respectively). Across all eight countries, the environmental and social performance categories have a lower compliance (34% and 44%, respectively) compared to economic performance (72% current compliance) and park management (55% compliance). A review of the root-causes indicates that the main compliance issue for 16 prerequisites and performance indicators outlined in the International EIP Framework seems mainly with the industrial park- and country-specific conditions. There is an opportunity to refine the formulation of five prerequisites and indicators outlined in the International EIP Framework. Across all 50 parks assessed, the following topics have the lowest current compliance: energy; local community outreach; environmental and park management and monitoring; waste and material use; and climate change and the natural environment. A low compliance with specific prerequisites and performance indicators under park management, economic, environmental, and social performance indicates a need by the industrial park for technical assistance. If high-performance industrial parks exist in a country, it implies that there is capacity in the country to develop an eco-industrial park. In this scenario, technical assistance should include a stronger focus on knowledge dissemination, sharing experiences, and peer-to-peer learning between industrial parks and the regulating authorities. Industrial parks managed by public–private partnerships and the private sector show a higher average EIP performance than industrial parks managed solely by the public sector. This seems to illustrate that industrial parks perform better if they are run like a private business or public–private partnership, rather than a government-managed initiative. This article is the first academic publication discussing the results from the application of the International EIP Framework with a large number of industrial parks in multiple countries. It is hoped that this article will encourage further EIP assessments to be undertaken in more industrial parks to assist in their transformation into eco-industrial parks.