  We discuss the spectrum of states of IIB supergravity on $AdS_5\times S^5$ in
a manifest $SU(2,2/4)$ invariant setting. The boundary fields are described in
terms of N=4 superconformal Yang-Mills theory and the proposed correspondence
between supergravity in $AdS_5$ and superconformal invariant singleton theory
at the boundary is formulated in an N=4 superfield covariant language.
