The quark-gluon plasma is a state of matter comprised of deconfined quarks and gluons that
exhibits remarkable properties. It has vanishingly small specific viscosity making it one of the
most perfect liquids known. It also has a record-high density, and is extremely opaque to transiting particles. Experimentally, the perfect liquid manifests itself in a collective flow of the produced particles that retains memory of the geometry of the initial-state energy density distribution, while the opacity is observed through the quenching of jets. This talk presents an overview of some of the historic hard-probe measurements at RHIC and the more recent results from the energy frontier with the LHC. It then discusses collective flow measurements from both RHIC and LHC, where we explore the limits of the perfect liquid behavior in the smallest quark-gluon plasma droplets.