Ion beams, after over 50 years of exploitation and optimization, have grown to be a key tool in modern tumour treatment. Currently over 50 ion therapy centres are in operation worldwide, next few tens are under construction. However, despite decades of experience, lack of in-vivo and in-situ monitoring methods disables full exploitation of excellent physical and biological properties of hadron beams. In my talk I will briefly remind the idea and the history of ion beam therapy. I will review methods of online range monitoring being developed by different group in the world, and focus on the Krak?w-Aachen-Katowice project.