This book constitutes the refereed proceedings of the 26th International Workshop on Computer Algebra in Scientific Computing, CASC 2024, which took place in Rennes, France, during September 2 - September 6, 2024. The 19 full papers included in this book were carefully reviewed and selected from 23 submissions. The annual International Workshop CASC 2024 aims to bring together researchers in theoretical computer algebra (CA), engineers, scholars, as well as other allied professionals applying CA tools for solving problems in industry and in various branches of scientific computing to explore and discuss advancements, challenges, and innovations related to CA.