This book provides new research on the patterns, functions and roles in disease of DNA methylation. Chapter One studies the disruption of DNA methylation patterns caused by exposure to environmental factors during the developmental period. Chapter Two presents transcriptional regulation by cytosine modifications through a broad concept of molecular sciences in physics, chemistry and biology, and suggests a complex network for cytosine modifications-mediated transcription depending on multiple factors. Chapter Three reviews the loss of Insulin-like growth factor 2 (IGF2) imprinting in human tumors, focusing especially on the mechanisms underlying this abnormality in epigenetic control; and summarizes recent progress on targeting this tumor specific imprinting abnormality as a novel anti-cancer approach.