Physical and chemical processes at the base of life and nature take place on timescales far away from our common sense. While our eyes cannot even distinguish the rapid flapping wings of a fly, the electronic motion occurs in less than few picoseconds (0.000000000001 s) i.e. more than ten billions times faster. In this book we focus on the electronic property called spin that is responsible for the magnetization in ferromagnets. A femtosecond (10^-15 s) laser source is exploited to unveil elementary interactions as electron-magnon and spin-phonon, the superdiffusive transport and coherent...