  Observing the neutral Hydrogen in galaxy clusters provides crucial insights
in the physical processes that influence the evolution of gas-rich galaxies as
they migrate from the lower-density filaments through the cluster outskirts
into to the higher-density central regions. The morphology-density relation,
the Buther-Oemler effect, and the observed HI deficiencies in the central
regions of galaxy clusters suggest that infalling galaxies experience a strong
transformation of their morphologies, star formation rates, and gas content.
The physical mechanisms that trigger and govern these transformations may
depend strongly on environment. This contribution aims to illustrate that the
morphological and kinematic characteristics of the cold gas provide a sensitive
tool to determine which mechanisms dominate in which environments.
