Venous thromboembolism (VTE), although relatively easy to treat, can often be difficult to diagnose noninvasively. Many different noninvasive tests are currently available to diagnose VTE, including both pulmonary embolism and deep venous thrombosis. Choosing a sensible diagnostic strategy requires an understanding of the each test’s strengths and drawbacks, as well as its applicability to the particular clinical situation. In this article, the principles of each test are discussed, and the diagnostic criteria are explained and critiqued. Specific algorithms are suggested for common clinical situations. In addition, the areas in which noninvasive testing does not yield accurate diagnoses are described. In those circumstances, invasive contrast examinations (venography or pulmonary angiography) may still be necessary. Finally, promising newer strategies are described that may, in the future, enable VTE to be diagnosed faster, easier, and less expensively.