The book "Mathematical Methods on Optimization in Transportation Systems" offers a comprehensive collection of selected works presented at the 7th EURO-Working Group Meeting on Transport at the Technical University of Helsinki in 1999. This publication includes 14 full articles that were chosen through a peer-review process. The topics covered range from the simulation of rail traffic to optimal congestion pricing and the modeling of transportation modes using preference data. The diversity of contributions highlights the broad interests of researchers in the field of transportation systems and their operation. Most articles are theoretical in nature and present models with hypothetical application examples, while some also describe practical applications and interesting results of well-known methods. Notably, half of the accepted works focus on the planning and operation of public transport.