This book presents the proceedings of the 12th IFToMM International Conference on Rotordynamics, held in Lahti, Finland, on June 22-26, 2026. This conference is a premier global event that brings together specialists from the university and industry sectors worldwide in order to promote the exchange of knowledge, ideas, and information on the latest developments and applied technologies in the dynamics of rotating machinery. The coverage is wide-ranging, including, for example, new ideas and trends in various aspects of bearing technologies, issues in the analysis of blade dynamic behavior, condition monitoring of different rotating machines, vibration control, electromechanical and fluid-structure interactions in rotating machinery, rotor dynamics of micro, nano and cryogenic machines, and applications of rotor dynamics in transportation engineering.