Title: Benchmarking Algorithms for Domain Generalization in Federated Learning. Abstract: In this paper, we present a unified platform to study domain generalization in the federated learning (FL) context and conduct extensive empirical evaluations of the current state-of-the-art domain generalization algorithms adapted to FL. In particular, we perform a fair comparison of nine existing algorithms in solving domain generalization {either centralized domain generalization algorithms adapted to the FL context or existing FL domain generalization algorithms } to comprehensively explore the challenges introduced by FL. These challenges include statistical heterogeneity among clients, the number of clients, the number of communication rounds, etc. The evaluations are conducted on three diverse datasets including PACS (image dataset covering photo, sketch, cartoon, and painting domains), iWildCam (image dataset with 323 domains), and Py150 (natural language processing dataset with 8421 domains). The experiments show that the challenges brought by federated learning stay unsolved in the realistic experiment setting. Furthermore, the code base supports fair and reproducible new algorithm evaluation with easy implementation.