The apparent distortions and alignments of faint galaxy images due to the gravitational lensing effect by the large-scale structure of the Universe is one of the potentially most powerful probes of cosmology. This so-called cosmic shear effect maps the matter distribution at different epochs and is thus sensitive to both the expansion history and the growth of structure. Forthcoming cosmic shear surveys such as the ESA Euclid mission will enable unprecedented insight into the properties of dark matter and dark energy, and
test the validity of general relativity on cosmological scales.

The anticipated high-quality measurements of cosmic shear require an accurate understanding and treatment of systematic effects. The major astrophysical effect that contaminates the cosmic shear signal is the intrinsic alignment of galaxies. During their formation and evolution, galaxies are subjected to tidal forces exerted by the surrounding large-scale structure, which causes the galaxies to align with the matter distribution and neighbouring galaxies. These alignments can exactly mimic the gravitational lensing signal and have been demonstrated to potentially yield a systematic signal that is up to two orders of magnitude above the statistical errors expected for Euclid. To date, observational constraints are weak and models simplistic, so that a major effort is needed to ensure the success of the Euclid mission and other cosmic shear surveys.

The planned workshops will bring together leading observational, theoretical, and numerical expertise on intrinsic alignments, with the goal to decisively advance the understanding of this astrophysical effect.

Full team proposal