Mostly Harmless could refer to...

* ''Literature/MostlyHarmless'', a sequel book and {{catch phrase}} in ''Franchise/TheHitchhikersGuideToTheGalaxy''
* ''Series/MostlyHarmless'', a public-access sketch comedy show from Connecticut, U.S.A.
* ''Roleplay/MostlyHarmless'', a {{Livejournal}} roleplay set in the [=H2G2=] universe