The length of each contract has not been disclosed by the Gunners.
Cazorla, 29, joined Arsenal from Malaga in 2012, while 23-year-old Ramsey arrived at the Emirates Stadium from Cardiff City in 2008.
Zelalem, 17, made his senior debut earlier this season after graduating from the club's youth academy. This deal represents his first professional contract.
"We are very pleased that Santi Cazorla, Aaron Ramsey and Gedion Zelalem have committed their futures to the club," manager Arsene Wenger told Arsenal's official website.
"Cazorla and Ramsey are absolutely key players for us, and this news is a boost to the whole club. Gedion is very young of course, but he has shown already that he has fantastic promise, and we all look forward to his development with us."
Arsenal's season continues on Saturday when they make the trip to Premier League title rivals Chelsea.