Peritonsillar abscess (PTA), also known as quinsy, is the most common deep space infection of the head and neck. It develops when acute tonsillitis or pharyngitis progresses beyond the tonsillar capsule into the peritonsillar space between the palatine tonsil and the superior pharyngeal constrictor muscle. Group A Streptococcus (Streptococcus pyogenes) is the most common causative organism, though polymicrobial infections with anaerobes (Fusobacterium, Prevotella, Peptostreptococcus) are frequent. The infection begins as peritonsillar cellulitis, with bacterial invasion causing edema, tissue necrosis, and purulent collection forming an encapsulated abscess. The abscess typically forms at the superior pole of the tonsil between the tonsillar capsule and the palatopharyngeus muscle. Progressive swelling causes uvular deviation to the contralateral side, trismus (restricted jaw opening) from inflammation of the pterygoid muscles, and potential airway compromise. Complications include extension to the parapharyngeal and retropharyngeal spaces, internal jugular vein thrombophlebitis (Lemierre syndrome), and aspiration of abscess contents.