The two-volume set LNAI 12854 and 12855 constitutes the refereed proceedings of the 20th International Conference on Artificial Intelligence and Soft Computing, ICAISC 2021, held in Zakopane, Poland, in June 2021. Due to COVID 19, the conference was held virtually. The 89 full papers presented were carefully reviewed and selected from 195 submissions. The papers included both traditional artificial intelligence methods and soft computing techniques as well as follows: -        Neural Networks and Their Applications   -        Fuzzy Systems and Their Applications   -        Evolutionary Algorithms and Their Applications   -        Artificial Intelligence in Modeling and Simulation   -        Computer Vision, Image and Speech Analysis -        Data Mining   -        Various Problems of Artificial Intelligence -        Bioinformatics, Biometrics and Medical Applications