Not Quite the Ingenue: The Development of the Middle-Aged Female Character in Musical Theatre is an exploration of the influences which have defined the function of middle-aged female characters within the musical theatre genre. This author was cast in the role of Arlene MacNalley, a forty-three year old woman, in the University of Central Florida's fall 2006 production of the musical Baby. Preparation for performance of this thesis role required identification of the traits and factors which would be vital for a realistic and relevant portrayal of Arlene. This document provides the reader with a working definition of middle age. It also furnishes a sampling of types, or stereotypes, of middle age female characters in musicals. The major thrust of the document emphasizes researching and understanding the importance of key socio-economic events' influence on the creation, direction, or depiction of middle-aged female characters. Three distinct characters are used to develop this theory, Aunt Eller in Oklahoma!, Dolly Levi in Hello, Dolly! and Arlene MacNalley in Baby. Further analysis within the thesis details essential differences between the original version of Arlene and the updated 2006 version of Arlene portrayed in the University of Central Florida's production of Baby. Conclusions drawn from the research, performance and writing processes indicate an increasing significance for the middle age female character as the genre of musical theatre continues to develop.