The preoperative use of botulinum toxin A has increased in recent years. It is recommended for complex hernias as an adjuvant to facilitate primary fascial closure and to avoid the component separation technique by inducing paralysis of the lateral abdominal wall muscles. This approach has shown promising results. This chapter summarizes the scientific background, including indications, dosing, injection sites, preoperative effects, and postoperative outcomes of botulinum toxin application.