In this paper, we study the asymptotic behavior of the Hermite
polynomials $H_{n}((2n+1)^{1/2}z)$ as $n\rightarrow \infty$. A
globally uniform asymptotic expansion is obtained for $z$ in an
unbounded region containing the right half-plane Re $z \geq 0$. A
corresponding expansion can also be given for $z$ in the left
half-plane by using the symmetry property of the Hermite
polynomials. Our approach is based on the steepest-descent method
for Riemann-Hilbert problems introduced by Deift and Zhou.