Background: Carbonic anhydrases (CAs), which catalyzeCO2hydration to bicarbonate and protons, have been suggested to regulate potassium homeostasis and endocochlear potential in the mammalian cochlea. Sixteen mammalianCAisozymes are currently known. To understand the specific roles ofCAisozymes in the inner ear, a systematic survey was conducted to reveal temporal and spatial expression patterns of all 16CAisozymes during inner ear development.Results: Our quantitative reverse transcriptase‐polymerase chain reaction results showed that different tissues express unique combinations ofCAisozymes. During inner ear development, transcripts of four cytosolic isozymes (Car1,Car2,Car3, andCar13), two membrane‐bound isozymes (Car12andCar14), and twoCA‐related proteins (Car8andCar11) were expressed at higher levels than other isozymes. Spatial expression patterns of these isozymes within developing inner ears were determined by in situ hybridization. Each isozyme showed a unique expression pattern during development. For example,Car12andCar13expression closely overlapped withPendrin, an anion exchanger, whileCar2overlapped withNa‐K‐ATPasein type II and IV otic fibrocytes, suggesting functional relationships in the inner ear.Conclusions: The temporal and spatial expression patterns of eachCAisozyme suggest unique and differential roles in inner ear development and function.Developmental Dynamics 242:269–280, 2013. © 2012 Wiley Periodicals, Inc.