This book constitutes the thoroughly refereed post-conference proceedings of the 34th International Workshop on Languages and Compilers for Parallel Computing, LCPC 2020, held in Delaware, NE, USA, in October 2021. Due to COVID-19 pandemic the conference was held virtually. The 9 revised full papers were carefully reviewed and selected from 11 submissions. The conference covers all aspects of languages, compiler techniques, run-time environments, and compiler-related performance evaluation for parallel and high-performance computing. The scope of the workshop encompasses foundational results, as well as practical experience reports and bold new ideas for future systems.