Photodynamic therapy is a treatment that uses a combination of light-absorbing photosensitizers and dissolved oxygen to kill cancer. One specific limitation of photodynamic therapy is that the visible light used for photosensitizer excitation has a short tissue penetration depth of several millimeters. This limits the application of photodynamic therapy to surface cancers in the absence of a technique to illuminate deeper tissue. Efforts to extend tissue depth to which photodynamic therapy can be applied have been attempted with use of up-conversion and persistent-luminescent nanoparticles that absorb near infrared light and emit visible light for photosensitizer excitation, yet an initial excitation with an external light source is still required. More recently, systems employing chemiluminescence as an excitation energy source designed to bypass the use of external light have been developed and investigated as potential agents that could overcome the problem of achieving photodynamic therapy in deep tissue. We wish to provide an overview of several systems that have been recently reported that employ both radiative and non-radiative chemiluminescent energy transfer for photosensitizer excitation that have been developed in the hope of achieving “dark” photodynamic therapy. This article reviews several of these important new developments in the design of photodynamic therapeutic systems that utilize chemiluminescence.