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 DEGREES-15 s) laser source is exploited to unveil elementary interactions as electron-magnon and spin-phonon, the superdiffusive transport and coherent collective oscillations. The main targets are not only understanding fundamental physical aspects but also the development of new ideas for technological devices as magnetic tunnel junctions and memory bits operating in an unexplored temporal regime. Two main timescales can be individuated: the femtosecond one in which the ultrafast demagnetization takes place and the picosecond one where we are able to invert the polarity of a magnet using light. For a better comprehension a wide part is dedicated to the explanation of the experimental techniques and to the state of the art in the