  One of the fundamental properties of the quark-gluon plasma (QGP), the
equation of state, is a subject of extensive studies in lattice QCD and an
essential requirement for the correct hydrodynamic modeling of heavy-ion
collisions. Lattice QCD provides first-principle calculations for the physics
in the non-perturbative regime. In this contribution, we report on recent
progress by the HotQCD collaboration in studying the 2+1 flavor equation of
state on lattices with the temporal extent N_tau=6, 8, 10 and 12 in Highly
Improved Staggered Quarks (HISQ) discretization scheme. Comparisons with
equation of state calculations with different fermion actions are also
discussed.
