This book provides an update on genomics, effectors and pathogenicity factors toward a better understanding of phytoplasma-host metabolic interactions. It offers a comprehensive overview of biological, serological and molecular characterization of the phytoplasmas, including recently developed approaches in diagnostics, such as transcriptomics studies, which have paved the way for analyzing the gene expressionpattern in phytoplasmas on infection and revealed the up-regulation of genes associated with hormonal response, transcription factors, and signaling genes. Although phytoplasmas remain the most poorly characterized pathogens, recent studies have identified virulence factors that induce typical disease symptoms and have characterized the unique reductive evolution of the genome. Reviewing the advances in cultivation in axenic media together with the perspectives for future research to reduce the global incidence of these pathogens and the associated agricultural losses, the book is a valuable resource for plant pathologists, researchers in agriculture and PhD students.