A variety of mass preserving moving boundary problems for the thin film equ
ation, u(t) = -(u(n)u(xxx))(x), are derived (by formal asymptotics) from a
number of regularisations, the case in which the substrate is covered by a
very thin pre-wetting film being discussed in most detail. Some of the prop
erties of the solutions selected in this fashion are described, and the ful
l range of possible mass preserving non-negative solutions is outlined.