  Transmission spectroscopy facilitates the detection of molecules and/or
clouds in the atmospheres of exoplanets. Such studies rely heavily on
space-based or large ground-based observatories, as one needs to perform time-
resolved, high signal-to-noise spectroscopy. The FORS2 instrument at ESO's Very
Large Telescope is the obvious choice for performing such studies, and was
indeed pioneering the field in 2010. After that, however, it was shown to
suffer from systematic errors caused by the Longitudinal Atmospheric Dispersion
Corrector (LADC). This was successfully addressed, leading to a renewed
interest for this instrument as shown by the number of proposals submitted to
perform transmission spectroscopy of exoplanets. We present here the context,
the problem and how we solved it, as well as the recent results obtained. We
finish by providing tips for an optimum strategy to do transmission
spectroscopy with FORS2, in the hope that FORS2 may become the instrument of
choice for ground-based transmission spectroscopy of exoplanets.
