Tumors of the retroperitoneum are either in very close relation to the lumbosacral plexus and its branches or originate from the plexus itself. This warrants very meticulous dissection techniques and monitoring if a function-sparing or minimally invasive approach is preferred to “excision with clean margins.” Nerve surgeons are used to this kind of dissection; however, they are sometimes not so familiar with intrapelvic dissection and the retroperitoneal space. This chapter aims to outline basic relevant anatomy and technique for transabdominal approaches and describes a systematic selection process for surgical access routes based on landmarks. We list different approach choices from anterior and lateral as well as its dorsal and caudal approach extensions, which can be combined in a modular way.