Serum tumor markers play a critical role in the diagnosis, staging, risk stratification, and surveillance of patients with testicular germ cell tumors (GCTs). Production of the oncofetal substances α fetoprotein and human chorionic gonadotropin can aid the diagnosis of testicular GCTs, and specific patterns of marker elevation can be used to determine the type of tumor, particularly as it pertains to nonseminoma. These markers, in addition to lactate dehydrogenase, have been incorporated in the standard TNM staging system for testicular tumors; the S stage category corresponds to serum elevation of these proteins. Furthermore, the degree of serum tumor marker elevation has been incorporated into standardized patient risk groupings, which are used to guide therapeutic management. The rate of tumor marker decay after radical orchiectomy is an important index to monitor, as a slow decline might be indicative of metastatic disease and should prompt a thorough systemic survey. The rate of tumor marker decline is already being utilized in the setting of metastatic GCTs to determine response to chemotherapy, and has been used in some scenarios to individualize the type of chemotherapy patients received. Compared to any other solid organ malignancy, the role of serum tumor markers in GCT is unprecedented; these markers are instrumental in the diagnosis and management of testicular GCT.