  We present an overview of the current state of understanding of the early
time dynamics of high-energy heavy-ion collisions, emphasizing recent
developments and connections between the physics of the initial state and that
of hard probes in heavy-ion collisions. Based on a weak-coupling description,
we first establish a microscopic picture of the early time dynamics and
equilibration process and subsequently discuss their macroscopic manifestations
along with a novel macroscopic description of the pre-equilibrium phase. Some
phenomenological consequences concerning the role of the pre-equilibrium phase
in large (AA) and small (pp/pA) collision systems are briefly discussed along
with open questions and opportunities for future improvements.
