Development of new therapeutic drug delivery systems is an area of significant research interest. The ability to directly target a therapeutic agent to a tumor site would minimize systemic drug exposure, thus provide the potential for increasing the therapeutic index. Photodynamic Therapy (PDT) in cancer treatment involves the uptake of a photosensitizer by cancer tissue followed by a photoirradiation. The selectivity of PDT as an anti-cancer treatment relies on the local generation of cytotoxic reactive oxygen species in the tumor, mainly singlet oxygen (1O2), due to both preferential uptake of the photosensitizer by malignant tissue and subsequent localized light irradiation. Selective accumulation of the photosensitizers by cancer cells or neo-vasculature is required to avoid collateral damage. Using nanoparticles as photosensitizers carriers is very promising since these nanomaterials can satisfy all the requirements for an ideal PDT: they can be functionalized onto their surface to target cancer cells or neo-vasculature, their chemical structure can be modulated to modify the plasmatic lifetime, and they can allow the diffusion of molecular oxygen to produce reactive oxygen species upon laser light exposure. This review describes and compares the different types of nanoparticles that can up to now be used for PDT applications: biodegradable polymer-based, ceramic-based, metallic and multifunctional nanoparticles that can associate imaging agents and targeting units. The nanoparticles are described in terms of drug loading, entrapment efficiency, stability, photocytotoxic efficiency, biodistribution and therapeutic efficiency for diagnostis and therapy. The latest results on the improvement of the photophysical properties will be also developed (biphotonic absorption, up conversion).