Neutron waves in a reflected reactor are analyzed using the two-group diffusion equation. The solution is composed of a transient which disappears within a few milliseconds, a steady-state part, and an oscillatory part. The last is comprised of four terms corresponding to four waves: two propagating waves and two reflected waves. When a sinusoidal source of thermal neutrons is applied to a water-moderated multiplying medium, the source wave amplitude decays with a relaxation length equal to the diffusion length of the medium. A wave of fast neutrons is then produced by fission which is induced by the source wave. This fast-neutron wave carries the wave phenomenon across the core. The two propagating thermal-neutron waves are (a) the source wave, and (b) a wave of thermalized fission neutrons. The two reflected waves are the reflections of the two propagating waves. The amplitudes and phases of the four waves are calculated, together with those of the total wave which is the sum of the four partial waves. The agreement of the measured data of the total wave with the calculations is reasonable. Modulated poison and source oscillators were used for the experiments. The reactor response to both was essentially the same except in the region near the oscillators; while the first decreased the number of neutrons, the second increased their number.