Theranostics in nuclear medicine has traditionally referred to pairing a diagnostic scan with a matched radiopharmaceutical therapy. This review argues for a broader, target-centric framework. In this model, molecular imaging serves as an in vivo companion diagnostic that verifies target expression across the whole body and guides selection, initiation, and monitoring of targeted therapies. This paradigm extends beyond radiopharmaceutical therapy to include antibody-drug conjugates, immunotherapy, and endocrine therapy. As precision medicine evolves, theranostics is best understood as a clinical pathway linking target biology to treatment decisions through imaging.