After discussing the importance of the physical processes that are able to remove gas from galaxies, I will describe what are the so called "jellyfish galaxies" and what we can learn studying them, and I will show how integral-field spectroscopy allows us to investigate the rich physics involved. I will present results regarding the star formation activity, the multi-phase gas content and the link between the two in the disks and tails of these systems. Moreover, I will discuss the possible existence of a connection between gas stripping and AGN activity, and conclude with a number of open questions.