Radiometric analysis of carbon-14 (14C) by liquid scintillation counting (LSC) and gas proportional counting (GPC) is reviewed. Typical sample size requirements are discussed, together with the conversion of sample carbon to an appropriate product for the measurement of the β-particles emitted during 14C decay; in the case of LSC, it is benzene (C6H6) and in the case of GPC, it is carbon dioxide (CO2), acetylene (C2H2), methane (CH4), or ethane (C2H6); the discussion, however, centers on CO2, which is the most commonly used of the four. Current instrumentation is reviewed with emphasis on background reduction features and the consequent limits of detection. In the case of LSC, the background reduction features include enhanced passive shielding, anticoincidence (active) shielding, and various forms of pulse-shape analysis. For GPC, background reduction centers on passive shielding designs and anticoincidence shielding. Age calculations, including correction factors for fractionation and sample purity, are also discussed.