**Abstract**

This chapter focuses on basic facts and details of photodynamic therapy (PDT). PDT's ability to cause cytotoxicity has led to its applications for a variety of medical conditions other than cancer treatment. This adaptable technology has some advantages in treating severe illness situations such as cancer, alopecia, angina pectoris, and periodontitis. It stands out even more because of the interaction of three elements: light, a photosensitizer (PS), and cellular oxygen. By preventing PS accumulation in normal vegetative cells, targeted photodynamic therapy plays an important role in achieving better accumulation of PS in a specific area. This section discusses various types of targeting methods, such as active targeting, passive targeting, and peptidemediated targeting. Aid in both diagnosing and curing diseases, gaining widespread acceptance. It is a promising therapeutic approach with a lot of potential.

**Keywords:** photodynamic therapy, porphyrin photosensitizers, targeted drug delivery, theranostics, photodynamic antimicrobial chemotherapy
