The possibility of tracking particles in space and time has attracted a lot of attention in the last few years, it is now part of the CMS and ATLAS upgrade for HL-LHC and it is considered the baseline tracking system at FCC and at the next muon collider.
In this talk, I will review the progress towards the development of Silicon sensors able to track particles in 4D with a precision of ~ 10 microns and ~ 10 picoseconds. I will show why thin Silicon sensors with moderate internal gain are a very promising technology to achieve this goal, and how we can make this technology radiation tolerant so that sensors can work after being exposed to fluences well above 1E15 n/cm2.