  Multilinear interpolation is a powerful tool used in obtaining strong type
boundedness for a variety of operators assuming only a finite set of restricted
weak-type estimates. A typical situation occurs when one knows that a
multilinear operator satisfies a weak $L^q$ estimate for a single index $q$
(which may be less than one) and that all the adjoints of the multilinear
operator are of similar nature, and thus they also satisfy the same weak $L^q$
estimate. Under this assumption, in this expository note we give a general
multilinear interpolation theorem which allows one to obtain strong type
boundedness for the operator (and all of its adjoints) for a large set of
exponents. The key point in the applications we discuss is that the
interpolation theorem can handle the case $q \leq 1$. When $q > 1$, weak $L^q$
has a predual, and such strong type boundedness can be easily obtained by
duality and multilinear interpolation.
