In this talk I will first review a long-standing discrepancy between the neutron lifetime as measured in beam and in bottle experiments. If this discrepancy is not due to a systematic error, it may be due to novel mechanisms for neutron transmutation into new, as yet unknown elementary particles. These particles would be electrically neutral, or so-called “dark”. We will explain several scenarios for the possibility of neutron transmutation into dark particles. For example, in one interesting scenario the products of the neutron transmutation include a monochromatic photon with energy in the range 0.782 MeV–1.664 MeV and this is predicted to occur in 1% of all neutron decays. We will describe recent theoretical developments as well as ongoing and planned experiments looking directly to establish or rule out the “dark decay” hypothesis.