microRNAs (miRNAs) are small noncoding RNAs that regulate various biological
phenomena, such as development and homeostasis. The dysregulation of miRNA leads to
disease progression, particularly of cancer. Recently, circulating miRNAs have been observed
in human body fl uids. Furthermore, miRNAs have been shown to be located inside exosomes,
which are small membrane vesicles, and these exosomal miRNAs are proposed to be
novel mediators of cell–cell communication. Although the clinical and industrial importance
of this research is promising, this research fi eld is still just beginning. The purpose of
this book is to inform the readers of recent advances in the isolation, puri fi cation, and analysis
of circulating miRNAs from a variety of sources for research. This book is divided into
three main topics. The fi rst involves the study of secretory miRNAs in cell–cell communication,
and the second, the study of circulating miRNAs in body fl uids. The last describes the
novel techniques used to study circulating miRNAs.