This book constitutes the refereed proceedings of the Third IFIP WG 1.8 International Conference on Topics in Theoretical Computer Science, TTCS 2020, held in Tehran, Iran, in July 2020. The conference was held virtually due to the COVID-19 pandemic.

The 8 papers presented in this volume were carefully reviewed and selected from 24 submissions. They focus on novel and high-quality research in all areas of theoretical computer science, such as algorithms and complexity; logic, semantics, and programming theory; and more.