This book constitutes the proceedings of the 18th IFIP WG 10.3 International Conference on Network and Parallel Computing, NPC 2021, which was held in Paris, France during November 3-5, 2021. The 20 papers presented in this volume were carefully reviewed and selected from 62 submissions. They were organized in topical sections as follows: algorithms and applications; system software and resource management; storage; and networks and communications.