  The hydrodynamic limit for the Boltzmann equation is studied in the case when
the limit system, that is, the system of Euler equations contains contact
discontinuities. When suitable initial data is chosen to avoid the initial
layer, we prove that there exists a unique solution to the Boltzmann equation
globally in time for any given Knudsen number. And this family of solutions
converge to the local Maxwellian defined by the contact discontinuity of the
Euler equations uniformly away from the discontinuity as the Knudsen number
$\varepsilon$ tends to zero. The proof is obtained by an appropriately chosen
scaling and the energy method through the micro-macro decomposition.
