Masculine nouns that end in –o form the plural by changing the –o into an –i. Feminine nouns that end in –a form the plural by changing the –o into an –e. Both masculine and feminine nouns that end in –e form the plural by changing the –e into an –i. Here are some examples:

libro (LEE-broh) changes to libri (LEE-bree)

amico (ah-MEE-koh) changes to amici (ah-MEE-chee)

gatto (GAHT-toh) changes to gatti (GAHT-tee)

sorella (soh-REHL-lah) changes to sorelle (soh-REHL-leh)

casa (KAH-zah) changes to case (KAH-zeh)

tazza (TAHTS-sah) changes to tazze (TAHTS-seh)

dottore (doht-TOH-ray) changes to dottori (doht-TOH-ree)

stazione (stahts-see-YOH-nay) changes to stazioni (stahts-see-YOH-nee)

cane (KAH-neh) changes to cani (KAH-nee)