The ionospheric D-region (~60 km up to ~95 km) and the corresponding neutral atmosphere, often refered to as the mesosphere-lower-thermosphere (MLT) are challenging and costly to probe in-situ. Therefore, remote sensing techniques have been developed over the years. One of these is based on VLF (Very low frequency, 3-30 kHz) electromagnetic waves generated by various natural and manmade sources. VLF waves propagate within the Earth-ionosphere waveguide, and are extremely sensitive to perturbations occurring in the D-region along their propagation path. Therefore, measurements of these signals serve as an inexpensive remote sensing technique for probing the lower ionosphere and the MLT region. This paper reviews the use of VLF narrowband (NB) signals (generated by man-made transmitters) in the study of the D-region and the MLT for over 90 years. The fields of research span time scales from microseconds to decadal variability, and incorporate lightning-induced short term perturbations; extraterrestrial radiation bursts; energetic particle precipitation events; solar eclipses; lower atmospheric waves penetrating into the D-region; sudden stratospheric warming events; the annual oscillation; the solar cycle; and finally, the potential use of VLF NB measurements as an anthropogenic climate change monitoring technique.