A method for setting a barrier within a wellbore comprises deploying a first plug assembly (16) into a wellbore on a running string, wherein the first plug assembly comprises an extendable arrangement (24), and then setting the first plug assembly within the wellbore by extending the extendable arrangement. A settable medium is injected via the running string into the wellbore above the first plug assembly. To be accompanied, when published, with FIG. 1F