Complete splenic flexure mobilization (CSFM) is an important step in left-sided colorectal resections. The aim is to achieve adequate oncological resection margins with complete mesocolic excision and to allow a tension free anastomosis for gastrointestinal continuity. Colorectal surgeons typically perform CSFM by one of three approaches (anterior, medial or lateral) in order to divide the peritoneal ligaments connecting the left colon. CSFM has minimal impact on post-operative outcomes and may have rare complications including risk of injury to pancreas duodenum, left branch of middle colic artery, marginal artery, spleen, inferior mesenteric vein, or left ureter. This video outlines the steps to perform CSFM by the medial trans-mesocolic approach. The patient is positioned in lithotomy and ports placed to triangulate towards the left upper quadrant. The first step involves exposure of the duodenal-jejunal flexure. Adhesions around the duodenal-jejunal flexure are taken down to reveal the inferior mesenteric vein. The inferior mesenteric vein is ligated at the lower border of the pancreas. Medial to lateral dissection begins inferior to the inferior mesenteric vein above Gerota’s fascia. Dissection continues until the left colonic wall is visualized. The lesser sac is then entered inferiorly through the avascular window in the transverse mesocolon. The pancreaticocolic ligament is divided which connects the dissection created earlier to the lesser sac. The greater omentum is then divided above the transverse colon to enter the lesser sac. Dissection is continued laterally towards the splenic flexure. Lateral dissection is continued through the left paracolic gutter. The planned surgical resection is continued.