  We discuss a number of prominent theoretical challenges in the physics of
ultrarelativistic heavy ion collisions, and review some recent attempts to
tackle them. These examples cover most stages of the collision process, but
emphasis is given to approaches that rely on first principles methods or
well-established Effective Field Theory frameworks. The topics discussed in
most detail include the early dynamics of a collision as well as the properties
of quark gluon plasma in thermal equilibrium.
