  Heavy quarkonium continues to play a central role in the study of nuclear
matter under extremes of temperature and density in relativistic heavy-ion
collisions. In this talk I report on recent developments in the theoretical
description of quarkonium in-medium dynamics using the open-quantum systems
approach. Not only does it provide a clear interpretation of the imaginary part
of the complex heavy-quark potential but also reveals that a subtle interplay
between screening and wavefunction decoherence is responsible for the melting
of heavy quarkonium states.
