Accelerated protons and heavy charged particles can be used to effectively treat deep-seated malignant tumors and arterioveaous malformation. Because of its extremely encouraging clinical outcome, this new form of particle therapy has been gradually progressing from investigational modality into hospital-based clinical practise. For nearly 50 years, the success in the development of this advanced technology was based on sound theoretical backgrounds, many radiation biology experiments, advances in innovative technologies, and experimental clinical work. There are now totally 16 proton treatment centers world-wide; the number is now known to be at least doubled in the next 3-5 years. The speed of the proliferation of the new modality speaks well the confidence the scientists and radiation oncologists have on proton beam therapy.