The Fabry-Perot interferometer (FPI) traditionally has been used to examine either small spectral ranges or relatively imple spectra. Recently, however, studies have shown that the FPI can be competitive with the Michelson interferometer ver extended spectral ranges. This paper describes a relatively new FPI technique in which one of the étalon plates is moved over a large optical distance while the other remains fixed, thus exploiting the multiplex advantage of the instrument. we have chosen to call this instrument the multiplex Fabry-Perot interferometer (MFPI). It is shown that this technique could be useful for the remote sensing of minor atmospheric species because the MFPI, like a Michelson interferometer, has the ability to examine large spectral regions at high resolution but retains the small size of the FPI.