This book presents a common principle of actions of long noncoding RNAs (lncRNAs) from points of view at the atomic, molecular and cellular levels. At the atomic level, chemical studies of ribonucleic acids explain the chemical behavior of lncRNAs. Structural biological analysis of lncRNAs and its binding proteins also reveal the precise mechanisms of their actions. Molecular biological approaches lead to insights into molecular mechanisms of these lncRNA actions. At the cellular or individual level of analysis, we grasp the biology and medicine of lncRNAs. These three layers of approaches are thoroughly new and produce novel insights into functions of lncRNAs in living cells. The book consists of five parts: 1) Bioinformatics and other methodologies for lncRNAs, 2) Atomic and molecular structures of lncRNAs, 3) Molecular functions of lncRNAs, 4) Biological actions of lncRNAs, and 5) Potential outcomes for clinical medicine. These sections connect well and work synergistically. The book is for researchers whose specialty is RNA biology and chemistry and also for advanced students at the graduate and undergraduate levels. Readers can grasp the leading edge of lncRNA studies in a comprehensive manner and are inspired to pursue their own particular interests.