The determination of atmospheric composition trends in the upper troposphere lower stratosphere (UTLS) is still highly uncertain. The project Observed Composition Trends And Variability in the UTLS (OCTAV-UTLS) will use different coordinate systems (for example, horizontal distance to the sub-tropical jet and vertical distance to the tropopause) to study the large spatial and temporal variability caused by competing transport, chemical, and mixing processes near the tropopause. The goal of this ISSI project is to combine satellite, aircraft, balloon and ground-based observations with meteorological reanalysis in a physical consistent way in order to understand the impact of the dynamical and/or chemical processes driving the natural variability on the observed UTLS trends by the different sensors on different platforms.