A multilayer-mirror interferometer for very cold neutrons has been in
progress for five years. This interferometer is analogous to a classic
al Mach-Zehnder interferometer using multilayer mirrors as optical ele
ments. The conditions required for the multilayer interferometer are p
resented, including mirror perfection and mirror-position accuracy. Pe
rformance tests are discussed such as mirror characteristics, mirror-p
osition adjustments and the interference pattern using neutrons.