In the last decades, the knowledge on the etiology of venous thromboembolism (VTE) has increased tremendously. In approximately half of patients presenting with VTE, one or more thrombophilic defects can be identified. This has led to widespread testing for thrombophilia, despite the fact that, at present, it is unclear whether this should have therapeutic consequences. Here we review the currently established hereditary and acquired thrombophilic defects, and focus on the pros and cons of testing in the setting of VTE. Thrombophilia is defined as a disorder associated with an increased tendency to venous thromboembolism (VTE). Thrombophilia can be acquired, such as in patients with cancer, or congenital, in which case a defect in the coagulation system is hereditary. Egeberg was the first to use the term thrombophilia in 1965, when he described a Norwegian family that had a remarkable tendency to VTE, based on a deficiency of antithrombin. Since then, various laboratory abnormalities, both hereditary and acquired, have been discovered that increase the risk of VTE. This article reviews the currently established thrombophilic abnormalities and discusses the potential usefulness and implications of testing for thrombophilia.