Among different types of labeling, ¹³C-labeled compounds are the most demanding in organic chemistry, life sciences and materials design. However, ¹³C-labeled organic molecules are very difficult to employ in practice due to extreme cost. The rather narrow range of labeled organic starting materials and the absence of universal synthetic building units further complicate the problem and make utilization of ¹³C-labeled molecules hardly possible in many cases. Here we report a versatile approach for ¹³C₂-labeling of organic molecules starting with ¹³C elemental carbon: ¹³C carbon is applied for the synthesis of calcium carbide (Ca¹³C₂), which is subsequently used to generate acetylene-a universal ¹³C₂ unit for atom-economic organic transformations. Syntheses of labeled alkynes, O,S,N-functionalized vinyl derivatives, polymers and pharmaceutical substances were demonstrated. Elemental <sup>13<