Arsenal defender David Luiz has agreed a new one-year contract with the club.
Defenders Pablo Mari and Cedric Soares will also join the Gunners permanently at the end of their loan deals, from Flamengo and Southampton respectively.
Meanwhile, midfielder Dani Ceballos has extended his loan deal from Real Madrid until the end of this season.
“I am really happy that we will have these players in our squad for the future,” said the Premier League club’s technical director Edu.
“They have been part of the long-term technical plan [manager] Mikel [Arteta] and I have developed. They bring the right balance to our squad.”
Brazil centre-back Luiz, 33, joined the club from Chelsea last year but was sent off during Arsenal’s return to Premier League action, a 3-0 defeat at Manchester City, last week.
“David is a really important player for us. He has played most of our matches this season and has been important for the team,” added Edu.
“His passing, his communication with the team on and off the pitch – he helps everyone.”
Spanish centre-back Mari, 26, and Portugal right-back Soares, 28, will complete their moves when the transfer window opens next month.