Advances in medical technology have brought the use of photosensitizing materials and light for treating diverse ailments to a new level, with reduced adverse effects and enhanced therapeutic outcomes. This new book focuses on diffusion optical imaging, a non-invasive imaging technique that allows for real-time visualization of the treatment area, and explores its application for treating patients through various modes. The volume discusses photodynamic treatement for pharmacological intervention, breast cancer diagnosis using biophotonics, photothermal therapy for cancer with gold nanoparticles, photobiomodulation therapy for the brain, with a specific focus on its potential impact on neurodegenerative conditions such as Alzheimer's and Parkinson's disease, and more.