In recent years many European transport organisations have introduced and successfully operated Integrated Periodic Timetables (IPT, also: "synchronised timetables") in order to improve the travel quality and speed on public transport networks. This can be done by optimising the departure and arrival times of transport media (trains, buses etc...) in such a way that the loss times in a network (e.g. resulting from waiting, using slow trains or from detours) are minimised. In this article, we present OptiTakt, a tool for the timetable planner which was developed in a Ph. D. project at the University of Marburg and which has successfully been applied in several timetable development and improvement projects. The focus of this tool is on building timetables under realistic conditions, interactive timetabling, using multiple views on schedules and on simulation for infrastructure planning. An absolutely optimal IPT is only possible under certain infrastructure conditions, which normally cannot be expected for already existing networks. Thus the construction of an optimal IPT is both a computational and an infrastructural optimisation problem: From the mathematical point of view, heuristic algorithms are required for its solution whenever networks of realistic size are to be treated. However, similar algorithms can also be used to figure out the most effective improvements of the technical railway infrastructure in order to achieve optimal connections for the majority of travellers within the network.