Observations indicate that a signature of the quasi-biennial oscillation (QBO) in the tropical lower stratosphere can be seen in the mean temperature, mean zonal wind, ozone concentration, and tidal amplitudes in the MLT. The QBO is expected to vary with increasing greenhouse gases through changes in tropospheric wave sources and speeding up of the stratospheric circulation. The QBO also responds to perturbations in stratospheric aerosols from volcanic eruptions. This presentation will discuss the processes that lead to the QBO signal in the MLT and the potential impact of stratospheric QBO trends on the MLT.