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.

Invited talks.- Majority Spanning Trees, Cotrees and Their Applications.- New Transportation Problem on a Graph with Sending and Bringing-Back Operations.- Long papers.- Algorithms for Diameters of Unicycle Graphs and Diameter-Optimally Augmenting Trees.- On Short Fastest Paths in Temporal Graphs.- Minmax Regret 1-Sink Location Problems on Dynamic Flow Path Networks with Parametric Weights.- The Bike Sharing Problem.- Efficient Generation of a Card-based Uniformly Distributed Random Derangement.- Compact Data Structures for Dedekind Groups and Finite Rings.- Competitive Location Problems: Balanced Facility Location and the One-Round Manhattan Voronoi Game.- Faster Multi-Sided Boundary Labelling.- On the Geometric Red-Blue Set Cover Problem.- Fixed-Treewidth-Efficient Algorithms for Edge-Deletion to Interval Graph Classes.- $r$-Gathering Problems on Spiders: Hardness, FPT Algorithms, and PTASes.- An Improvement of Reed's Treewidth Approximation.- Homomorphisms to digraphs with large girth and oriented colorings of minimal series-parallel digraphs.- Overall and delay complexity of the CLIQUESand Bron-Kerbosch algorithms.- Computing $L(p,1)$-Labeling with Combined Parameters.- On Compatible Matchings.- Upward Point Set Embeddings of Paths and Trees.- 2-colored Point-set Embeddings of Partial 2-trees.- Better approximation algorithms for maximum weight internal spanning trees in cubic graphs and claw-free graphs.- APX-Hardness and Approximation for the $k$-Burning Number Problem.- Efficient Enumeration of Non-isomorphic Distance-Hereditary Graphs and Ptolemaic Graphs.- Physical Zero-Knowledge Proof for Ripple Effect.- Cyclic Shift Problems on Graphs.- Mathematical Characterizations and Computational Complexity of Anti-Slide Puzzles.