This book presents a state-of-the-art compilation of articles on the role of non-coding RNAs as pivotal molecules for establishing functional relationships between different organisms. It also describes how non-coding RNA molecules can act as dynamic communication devices and how they modulate the interaction between different kingdoms. It describes examples including viruses, bacteria, fungi, and higher organisms such as protozoa that are involved in pathogenic or symbiotic interactions, and the roles of different families of non-coding RNAs within these relationships. Each chapter provides readers molecular and functional insights, breaking down the subjacent mechanisms and exploring their functional implications and future applications. More than sixty years after the foundation of the “RNA tie club� by George Gamow, new roles for non-coding RNA molecules are starting to be revealed.