Thalassa is title of a late poem written by Irish Poet Louis MacNeice.

In biology, Thalassa is a genus of ladybird beetle.

Thalassa is a band which represented Greece at the Eurovision Song Contest 1998.

Thalassa is a fictional planet, a waterworld in Arthur C. Clarke's novel Songs of Distant Earth.

Thalassa is the name of an electoral ward in the City of Onkaparinga.

Thalassa is a notable long-running television program on the television channel France 3 that reports on all items of interest in the nautical, maritime and oceanic field.

Thalassa is a moon of the planet Neptune.

In Greek mythology, Thalassa ("sea") was a primordial sea goddess.

Panthalassa ("all seas") was the global ocean surrounding the supercontinent Pangea.