This article reviews the commonly used anticoagulants (warfarin and heparin) and associated recommended laboratory testing. Emphasis is on the various modes of International Normalized Ratio testing and associated variability (clinical laboratory, point of care, patient self-testing). Unfractionated heparin and well-recognized coagulation testing issues are reviewed. The newer anticoagulants (heparin analogs, direct factor Xa inhibitors, and direct thrombin inhibitors) and various applied coagulation laboratory testing and related issues are also discussed.