Stratéole 2 is an international collaboration to deploy constellations of equator-orbiting super pressure balloons to probe the Tropical Tropopause Layer (TTL) and equatorial lower stratosphere. The project comprises three flight campaigns in early 2019, late 2020 and late 2023 in which constellations of 5, 20 and 20 balloons will be launched from the Seychelle islands (4°S). The super pressure balloon system and flight control gondola, 'Euros' has been developed by CNES as a follow to the highly successful Concordiasi campaign in the Antarctic and Pre-Concordiasi campaign at the equator. There are two balloon configurations: a stratospheric configuration with 13m diameter balloons that will fly near 20km and a TTL configuration with 11m diameter balloons that will fly near 18km at the upper edge of the TTL. Flight durations of over 3 months are planned with a flight domain circling the equator and spanning from 20°S to 15°N. Scientific instruments are carried on a modular science gondola, 'Zephyr', developed at LATMOS, which is configurable to support up to four instruments per gondola, with each instrument combination chosen to target specific science questions. A suite of 12 instrument has been developed by both US and French institutions specifically for this project and consist of in situ measurements of aerosols, water vapor, methane, ozone, pressure, winds and temperature profiles, and remotely sensed measurements of temperature profiles, longwave radiation and cloud and aerosol backscatter. The scientific goals of Stratéole 2 are wide reaching and include investigating the dynamics and thermal structure of the TTL, dehydration of air entering the stratosphere, chemical and aerosol transport near the TTL, multiscale equatorial waves and largescale circulations such as the Quasi Biennial Oscillation (QBO).