So far, temporal variability in the geographical distribution of risks has been ignored in this book. Observed counts often corresponded to long time periods and geographical changes that could have happened during that time interval have been missed by such a long temporal aggregation. As a consequence, one could be missing important information on the evolution of the distribution of diseases that could be very relevant under an epidemiologic point of view. The main goal of this chapter is to include the temporal dimension into disease mapping studies so that we will be able to obtain a dynamic view of the geographical distribution of risks instead of a fixed picture for, sometimes long, periods of study.