Individual tumour molecular profiling and tacking dynamic evolution by treatment related selective pressure are crucial for clinical oncology. However, current tissue biopsy cannot represent spatial and temporal tumour heterogeneity due to sampling bias.  Liquid biopsy is an alternative way of tissue biopsy since it can represent comprehensive molecular signature from multiple distinct lesions and real time tracking is feasible by repeated longitudinal assay during course of treatment. This book describes current knowledge regarding pre-analytical issues including standardization of blood preparation, analytical variability, clinical application and regulatory agency approval issue, etc. Regarding targets in circulation, it focuses on circulating tumour cells (CTCs), circulating nucleic acid (ctDNA, cell free RNAs), extracellular vesicles, tumour educated platelets, and others (proteins, metabolites). The book will be a rich source of information and instruction for oncologists and offers stimulating ideas on prospects for further progress in this field.