Resolving the controversies surrounding the anatomical spread, clinical effectiveness and safety of erector spinae plane block (ESPB) versus paravertebral block (PVB) is crucial for optimizing postoperative pain management in thoracic and breast surgery. This review systematically examines evidence published between 1 January 2014, and 1 January 2025, regarding the clinical efficacy, anatomical mechanisms, and complication profiles of ESPB and PVB, with a specific focus on their application in video-assisted thoracoscopic and breast surgery. Both ESPB and PVB significantly reduce postoperative pain and opioid consumption compared to controls (p<0.05), thereby minimizing opioid-related complications. However, important controversies persist over their comparative analgesic performance and safety. Some studies report that PVB may provide superior analgesia, but it also carries a higher risk of complications, such as hematoma (2 cases in the PVB group, none in the ESPB group) and pneumothorax (observed with PVB but not reported with ESPB). ESPB is therefore considered safer due to its lower complication rate. Anatomical investigations reveal that ESPB exhibits multidirectional spread of local anesthetic: (1) cranio-caudal along the fascial plane, increasing the number of dermatomes covered and expanding the area of analgesia; (2) medial spread to the paravertebral space, which may enhance blockade of the ventral rami and improve analgesic reliability; (3) lateral diffusion toward the intercostal spaces, potentially influencing chest wall sensation; (4) spread to the dorsal rami, contributing to posterior thoracic analgesia; and (5) limited anterior extension, which has implications for the consistency of ventral ramus blockade. The clinical significance of these spread directions lies in their impact on the quality, extent, and predictability of analgesia, as well as the potential for reducing procedure-related risks compared to PVB. Given current uncertainties in anatomy and outcomes, immediate research priorities should include developing individualized ESPB protocols that account for anatomical variation and total local anesthetic dose, and validating these approaches through multicenter randomized trials. By clarifying these issues, this review aims to provide clinicians with focused, up-to-date evidence to guide block selection, optimize perioperative outcomes, and support the standardization of regional anesthesia protocols.