Liquid biopsy analyzes tumor-derived biomolecules circulating in blood and body fluids that reflect genetic, transcriptomic, proteomic, and metabolic tumor features. The principal analytes include circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), and extracellular vesicles (EVs), each representing distinct biological levels. CTCs provide comprehensive cellular information but are limited by extreme rarity. ctDNA enables highly sensitive genomic profiling and has achieved the most rapid clinical adoption. EVs, protected by lipid bilayers, can carry multi-omics cargo and are emerging as next-generation diagnostic platforms. Each analyte has inherent advantages as well as biological and technical limitations. As a result, reliance on a single analyte is increasingly insufficient for complex clinical questions. Recent strategies emphasize multi-analyte integration to enhance diagnostic accuracy and robustness. This chapter compares the biological characteristics, clinical potential, and limitations of CTCs, ctDNA, and EVs.