In the last few years, the study of effects induced by energetic particle (ion) beam on polymers has attracted growing attention, both for fundamental interest and for potential technological applications. Polyethylene terephthalate (PET) can be modified by neutron and proton irradiation because of effects on the molecular bonds due to radiation- solid interactions. Present book entitled "Radiation-Induced Polymer: Modification and Analysis" is based on analysis of in-air neutron and proton irradiated PET fibre. For neutron (4.44 MeV) irradiation, an Am-Be based laboratory neutron source was used while proton (3 MeV) irradiation was carried out in a specially fabricated external-beam line and fibre irradiation cell with the 3 MV Tandem Pelletron Accelerator at Institute of Physics, Bhubaneswar, India. The radiation-induced modifications in the physical and chemical properties of the PET fibre were investigated using X-Ray diffraction (XRD), Micro-Raman spectrometry (MRS), Thermogravimetry (TG), Differential scanning calorimetry (DSC), Laser diffraction (LD), Instron, Scanning electron microscope (SEM) techniques and can be very much useful for polymer scientists.