Transcriptomics refers to the study of the transcriptome, which is the complete set of RNA transcripts produced by the genome of a specific cell. This book provides an overview of the information that the transcriptome provides and how developments in transcriptomics has transformed our understanding of cell biology. This book is comprised of three parts. Part I serves as an introduction to describe the development of transcriptomics as a technique and the way by which it has enhanced our knowledge and provided a better understanding of the basic biology of cellular function. Part II of the book is written to understand the milestones and contributions of transcriptomics in understanding the dynamics of cancer biology. Part III provides an insight on how transcriptomics is helping us to understand microbes and host-pathogen interaction including bioremediation.