  This talk provides a summary of the results obtained by the HotQCD
collaboration on the equation of state and the crossover transition in 2+1
flavor QCD. We investigate bulk thermodynamic quantities - energy density,
pressure, entropy density, and the speed of sound over the temperature range
140 < T < 540 MeV. These results have been obtained on lattices of temporal
size N_tau = 6 and 8 and with two improved staggered fermion actions, asqtad
and p4. Our most extensive results are with masses of the two degenerate light
quarks set at m_l = 0.1 m_s corresponding to the Goldstone pion mass m_pi
between 220-260 MeV. In these simulations, the strange quark mass is tuned to
its physical value and constant values of m_l/m_s define lines of constant
physics. We also summarize the current state of results on observables
sensitive to the chiral and deconfining physics -- the light and strange quark
number susceptibilities, the chiral condensate and its susceptibility, and the
renormalized Polyakov loop. Our results indicate that the deconfinement and
chiral symmetry restoration occur in the same narrow temperature interval.
