Progress is reported on the following aspects of the integral neutron thermalization program: the design, construction, and operation of a facility for measuring low-energy neutron spectra by the pulsed-source method; the design, construction, and operation of a slow chopper facility for measuring low-energy and time-dependent neutron spectra; a theoretical and analytical program with primary emphasis on describing neutron lifetimes from the standpoint of determining irtegral properties of the moderator; and the developmert of general instrumentation and data-reduction procedures to mske the experimental program feasible. (B.O.G.).