Azkaban is a wizarding prison. It is guarded by dementors. Sirius Black was the first person to ever breakout of Azkaban. In Harry Potter and the Order of the Phoenix there is a mass breakout from Azkaban and ten high-security prisoners escape including Bellatrix Lestrange, Antonin Dolohov, and Agustus Rockwood.
 Known Break Outs of Azkaban
- Barty Crouch Jr. - c. Winter 1982
"About a year" after he was brought in, Crouch's parents hatched a plan in which he would trade places with his dying mother. Barty Crouch Sr., at the time the Head of the Department of Magical Law Enforcement, led Mrs. Crouch into Azkaban to visit. While there, she and Barty Jr. each drank Polyjuice Potion to take on each other's appearance, and Crouch Jr. departed with his father while his mother was left in his place to die 
- Sirius Black - July 1993
Cornelius Fudge came to visit Azkaban this summer, and gave a copy of his Daily Prophet to Sirius. On the front page, though, was a picture of the Weasley family that included Ron's pet rat, Scabbers. What Sirius alone knew was that Scabbers was actually an unregistered Animagus - Peter Pettigrew - who was also a Death Eater. An unregistered Animagus himself, Sirius transformed into a dog when the Dementors brought him food; in this state he was able to slip past them undetected and swim to shore .
- Antonin Dolohov, Augustus Rookwood, Bellatrix Lestrange, Rodolphus Lestrange, Rabastan Lestrange, Mulciber, and four other Death Eaters - January 1996
With the Ministry of Magic losing control of the Dementors, ten "high-security prisoners" were allowed to escape and re-join Voldemort (OP25; we know Mulciber, Rodolphus, and Rabastan are included as they were imprisoned in GF30, but fought in the Battle of the Department of Mysteries in OP35).
 Known Witches/Wizards In Azkaban
- Sirius Black - Sent to Azkaban without trial (GF27). He was accused of betraying James and Lily Potter to Voldemort, then blowing up Peter Pettigrew and a street full of Muggles, c. November 1981 (PA10). Escaped July 1993 (PA3)