In this book, Chapter One reviews recent fundamental studies about Type I photosensitisers for photodynamic therapy (PDT). Chapter Two reviews the general features of the antibacterial photodynamic inactivation of bacteria (aPDT) process to eradicate bacteria with the use of photosensitiser agents, and summarises the photobiological processes which are involved in the inactivation of microbiological cells like the formation of reactive oxygen species (ROS). Chapter Three studies the different applications of rose bengal and its perspective using in non-invasive biomedical techniques. Chapter Four introduces multi-phototherapy based on combined use of photosensitisers and photothermal agents. Chapter Five summarises recent studies in the field of photodynamic inactivation of pathogenic bacteria and fungi with the newly synthesised phthalocyanines. Chapter Six discusses the immobilisation of the photosensitisers on the solid surface for the application in the photooxidation reactions. Chapter Seven reviews vehicles, ways and new challenges for the improvement of photsensitisers delivery.