The Atlantic Meridional Overturning Circulation (AMOC) is a critical component of the climate system. Climate models have long predicted a slowing of the AMOC due to anthropogenic forcing, with a risk of passing tipping points in the future. The question of whether the AMOC is already weakening in response to global warming is still somewhat controversial. Continuous monitoring is only available for the past two decades, a period too short to tease apart contributions of natural variability and climate change. Reconstructions of AMOC strength going back further in time have different limitations which are debated in the literature. Here we review the state of this discussion. We conclude that the balance of multiple lines of evidence strongly supports a past and ongoing AMOC slowing in response to global warming.