Lanthanide-based carriers have emerged as powerful platforms for next-generation biomedical imaging, combining unique optical and magnetic features to address key limitations of conventional agents. Owing to their 4f electron configuration, lanthanide ions provide sharp emission lines, long lifetimes, high photostability, and strong paramagnetism, enabling high-resolution, multiplexed, and deep-tissue imaging with minimal photodamage. This review surveys recent advances across optical, X-ray, and magnetic resonance modalities, focusing on how material design influences performance. We examine representative carriers, such as lanthanide-doped nanoparticles, organic complexes, and lanthanide-binding proteins, and their roles in near-infrared (NIR) imaging (long-term single-particle tracking, molecular sensing, and NIR-II modalities), X-ray imaging (contrast media, scintillators, and persistent emitters for low-dose diagnostics), and magnetic resonance imaging (chemical and biosynthetic agents with enhanced relaxivity, specificity, and safety, including targeted protein constructs). We highlight molecular engineering and surface modification strategies that boost signal and biocompatibility, and discuss emerging directions such as artificial intelligence-enabled data analysis and the integration of multimodal probes to deliver integrated anatomical and functional information. While most advances are still at the proof-of-concept stage, lanthanide carriers show great potential for bridging materials science, biophysics, and clinical needs, and are reshaping biomedical imaging toward more precise, responsive, and personalized diagnostics.