The subject of this book is high order finite difference methods for time dependent PDE. The idea is to give an overview of the basic theory and construction principles by using model examples. The book also contains a general presentation of the techniques and results for well-posedness and stability, with inclusion of the three fundamental methods of analysis both for PDE in its original and discretized form: the Fourier transform, the eneregy method and the Laplace transform. Various types of wave propagation problems are treated in specific detail since high order methods are particularly effective for these problems.