Ao is a village in Väike-Maarja Parish, Lääne-Viru County, in northeastern Estonia.
Ao was attested in historical sources as Hackeueyde in 1536, Hackeweide in 1559, and Ao in 1732. The name comes from the noun (genitive: ) 'stick, twig, small branch'.
Notable people that were born or lived in Ao include the following: