  If $\mu $ is a positive Borel measure on the interval $[0, 1)$, the Hankel
matrix $\mathcal H_\mu =(\mu_{n,k})_{n,k\ge 0}$ with entries
$\mu_{n,k}=\int_{[0,1)}t^{n+k}\,d\mu(t)$ induces formally the operator
$$\mathcal{H}_\mu
(f)(z)=\sum_{n=0}^{\infty}\left(\sum_{k=0}^{\infty}\mu_{n,k}{a_k}\right)z^n$$
on the space of all analytic functions $f(z)=\sum_{k=0}^\infty a_kz^k$, in the
unit disc $\mathbb{D} $. In this paper we describe those measures $\mu$ for
which $\mathcal{H}_\mu $ is a bounded (compact) operator from $H^p$ into $H^q$,
$0<p,q<\infty $. We also characterize the measures $\mu $ for which $\mathcal
H_\mu $ lies in the Schatten class $S_p(H^2)$, $1<p<\infty$.
