Monte Carlo Search : first workshop MCS 2020 held in conjunction with IJCAI 2020 virtual event January 7 2021 : proceedings This book constitutes the refereed proceedings of the First Workshop on Monte Carlo Search MCS 2020 organized in conjunction with IJCAI 2020. The event was supposed to take place in Yokohama Japan in July 2020 but due to the Covid 19 pandemic was held virtually on January 7 2021. The 9 full papers of the specialized project were carefully reviewed and selected from 15 submissions. The following topics are covered in the contributions: discrete mathematics in computer science games optimization search algorithms Monte Carlo methods neural networks reinforcement learning machine learning The Search Algorithm for the Game of Bridge Stabilized Nested Rollout Policy Adaptation zoNNscan: A Boundary Entropy Index for Zone Inspection of Neural Models Ordinal Monte Carlo Tree Search Monte Carlo Game Solver Generalized Nested Rollout Policy Adaptation Monte Carlo Inverse Folding Monte Carlo Graph Coloring Enhancing Playout Policy Adaptation for General Game Playing.