At least 38 of the fission product isotopes are now known to be delayed-neutron precursors. The region of delay ed-neutr on emission for each fission product element is predicted successfully by recent mass formulas, and the neutron emission probability (Pn) can be approximately related to basic nuclear parameters. Using Pn values and calculated cumulative fission yields, it is possible to account for some features of gross delayed-neutron emission from various types of fission. Further significant progress in understanding delayed-neutron emission is expected in the near future when spectroscopic studies are made on delayed-neutron precursors.