Fast neutron therapy was introduced in London in 1970. The book gives an overview of the developments of the past 28 years, assesses the results of fast neutron treatment, and reviews the compiled clinical data worldwide. The authors describe the radiobiological profile of the neutron beams and evaluate the neutron RBE for secondary cancer induction, they introduce heavy-ion therapy, which combines high physical selectivity with the biological advantages of high-LET radiation for some tumor types, and finally they describe the very recent developments in Boron Neutron Capture Therapy (BNCT).