It is now well-known that the climate is changing, but the effects of climate change vary at different atmospheric levels. For example, climatemodels predict up to a 7K cooling of the stratosphere, but a warming of the troposphere of about 2K. Thus, it is of primary importance to detect and quantify such changes, and to identify and measure exchanges between atmospheric levels. Achieving this goal requires long-term data records documenting the atmosphere’s vertical temperature profile and chemical composition. Ideally, this data should reflect varying types of instruments and approaches (i.e., ground based observations, satellite data, andmodels). At an atmospheric station on Reunion Island, scientists are contributing to this data set (see Figure 1) using the systems at their disposal. There have been five main instruments available at the island in recent years. First, the systeme d’analyse par observation zenitale (SAOZ) is a UV-visible spectrometer providing total ozone (O3) and NO2 columns twice a day, at sunrise and sunset. This instrument has worked to this schedule since 1993. SAOZ data is being extensively used for the validation of satellite data. The multi-axis differential optical absorption spectroscopy instrument (MAXDOAS) is another UV-visible spectrometer designed to measure stratospheric and/or tropospheric columns of atmospheric trace gases NO2, BrO, HCHO, O3 , SO2, IO, and O4. This was installed in July 2004 andoperated continuously for a period of one year. In 2007, it is expected to resume operations. Third is a high-spectral-resolution Fourier-transform infrared spectrometer (FTIR) that provides quasi-simultaneous total column and/or vertical profiles of about 20 atmospheric species, including O3 , CO, N2O, OCS, HF, HCl, and HNO3. So far, this instrument has been operated as needed, rather than on a routine basis, with longer-term operation expected to begin in 2007. Next, a light detection and ranging (lidar) system based on the active emission of laser pulses into the atmosphere is Figure 1. Atmospheric parameters are measured at a variety of altitudes by an instrumental set developed at Reunion Island. Hatched rectangles and lines represent total column measurements and profiles, respectively. Radiometers are in blue, sondes in red, and lidar in green.