EOLSS Contributions are written at different levels of hierarchy:
The Theme-level chapter represents an overview that is addressed to a broad readership. The length of Theme-level contributions is about 30 pages on average.
A Topic-level chapter provides a broad summary and evaluation of the subjects covered by the Articles under the topic. The contributions are rendered accessible to advanced students who want to begin or advance their knowledge in a particular subject. The length of a Topic-level chapter is about 20 pages.
Most of the chapters in the EOLSS are written at this level. Articles cover a subject in depth and contain relevant and necessary details of the established knowledge for the specialists. They contain the latest advances and results in the subject area with indications of future trends.