This book constitutes the proceedings of the 15th International Conference on Algorithms and Computation, WALCOM 2021, which was planned to take place in Yangon, Myanmar in February/March 2021. The conference changed to an online format due to the COVID-19 pandemic. The 24 full papers included in this volume were carefully reviewed and selected from a total of 60 submissions. They cover diverseareas of algorithms and computation, such as approximation algorithms, algorithmic graph theory and combinatorics, combinatorial algorithms, combinatorial optimization, computational biology, computational complexity, computational geometry, discrete geometry, data structures, experimental algorithm methodologies, graph algorithms, graph drawing, parallel and distributed algorithms, parameterized algorithms, parameterized complexity, network optimization, online algorithms, randomized algorithms, and string algorithms.