Rambam - Book of Love - Laws of Reading the Shema - Chapter 4

This is the second book of the Mishneh Torah of the Rambam, Rabbi Moshe ben Maimon. Laws of Reading the Shema.
This chapter explains that women, slaves, children, and those preoccupied with their hearts are exempt from reciting the Shema. Those who marry a virgin are exempt until when, as are those who marry a non-virgin. Those whose relative dies and all those who attend to the deceased are also exempt. All those deemed ritually impure must recite the Shema and its blessings, as well as the decree of Ezra and his judgment concerning those who witnessed a seminal emission that did not persist.