This two-volume set CCIS 1981 and 1982 constitutes the refereed post-conference proceedings of the Third International Conference on Optimization, Learning Algorithms and Applications, OL2A 2023, held in Ponta Delgada, Portugal, in September 2023. The 66 revised full papers presented in these proceedings were carefully reviewed and selected from 162 submissions. The papers are organized in the following topical sections:Volume I:Machine learning; learning algorithms in engineering education; machine learning and data analysis in internet of things; optimization; optimization in the SDG context. Volume II:Computer vision based on learning algorithms; machine learning and AI in robotics; optimization in control systems design.