Epigenetic modifications comprise heritable gene expression changes that occur without alteration of the DNA sequence and 'co-act' with genetic factors to shape development processes and evolutionary trajectories. Multicellular organisms receive different types of environmental stimuli/stresses that trigger epigenetic modifications during development. These environmentally driven mechanisms represent an underlying cause of phenotypic diversity, especially in metazoans. This book aims to present some of the latest epigenetic insights into the development of metazoans (including humans) as an intersection between their ecology and evolution.