This collection contains the conference proceedings of the third Open Science Day organized by KU Leuven on 2 May 2023. The event consisted of two paper sessions focusing on reuse and reproducibility and novel Open Science approaches. In addition, researchers and service units of KU Leuven outlined how they apply and support open science practices during a poster session. The keynote lectures were given by Muki Haklay (University College London) and Thomas Margoni (KU Leuven).