  We construct generic spherically symmetric thin shells by using the
cut-and-paste procedure. We take considerable effort to make the analysis as
general and unified as practicable; investigating both the internal physics of
the transition layer and its interaction with "external forces" arising due to
interactions between the transition layer and the bulk spacetime. We
demonstrate in full generality that stability of the thin shell is equivalent
to choosing suitable properties for the material residing on the junction
interface. Applications to gravastars and wormhole geometries are also
explored.
