The past 20 years have witnessed a paradigm shift in magnetism: the traditional role of magnetic fields as the main tool to read and write magnetic information, has gradually been taken over by spin currents. Spin currents, the flow of net spin angular momentum carried by electrons in materials, have in fact a great advantage over magnetic fields. Whereas magnetic fields are difficult to localize and effective at controlling magnetism only down to the nanosecond regime, spin currents can operate at the temporal and spatial scales of the exchange and spin-orbit interaction, i.e. at the nanometer and femtosecond level.

In this talk, I will give an overview of the historical transition from magnetic fields to spin currents, both from the point of view of fundamental research as well as that of commercial technology. I will highlight how our improved understanding of how to create, control and detect spin currents has often led to the industrial realization of novel magnetic devices that have greatly impacted society. I will also describe how recent discoveries offer new promising routes towards the further advancement of spin-current based technology.

I will conclude by illustrating how the x-rays generated at last generation lightsources have recently been used to directly observe spin currents with nanometer and femtosecond resolutions, revealing the occurrence of unexpected and intriguing phenomena. These results are source of great excitement, and pave the way for future groundbreaking experiments at the newest synchrotrons and free electron lasers being built around the world.