Mouser may refer to:

A domestic cat used for hunting rodents, e.g. a farm cat or ship's cat.
Chief Mouser to the Cabinet Office, the official resident cat of the Prime Minister of the United Kingdom.
Mouser Electronics, an electronic component retailer.
Mouser, 1983 computer game from IBM about a cat who pushes blocks on mice.
A type of robot from the Teenage Mutant Ninja Turtles series created by Baxter Stockman.
A boss in the video game Super Mario Bros. 2 and recurring villain for cartoon segments of The Super Mario Bros. Super Show!.
A name for a fan of the band Modest Mouse.

Pipi or Pipis may refer to:

Plebidonax deltoides, an edible clam known as pipi in parts of Australia
Paphies australis, a mollusc endemic to New Zealand
Pipi A, a High Priest of Ptah during the Ancient Egyptian 21st Dynasty
Neterkheperre Meryptah called Pipi II, another 21st Dynasty High Priest of Ptah
Pipi, vocalist of the Ska band Ska-P
Pipi, a transcription (ΠΙΠΙ) into Greek of the Tetragrammaton
Pipi, slang word for urine in a number of European languages
Pipis, an alternative name for Berkaber