The book "Computer Simulation Studies in Condensed-Matter Physics XII" offers a comprehensive collection of contributions that emerged from a workshop focused on the latest developments in computer simulation in solid-state physics. This workshop brings together both experienced researchers and newcomers to discuss innovative techniques and current results. The collection includes both invited contributions and presentations from participants addressing various aspects of classical and quantum solid-state physics. The publication aims to make the results accessible to a broader audience in a timely manner and to promote ongoing discussion within the scientific community. Support from IBM Corporation is also acknowledged, as it contributed to the realization of the workshop.