The study of vertebrate embryonic development became a separate science in the early 1800s thanks to advances in microscopy. Embryologists collected and dissected specimens from chicken, frogs, turtles, fish, mice as well as humans, observed and documented the anatomy and physiology. These largely observatory work produced many of the important concepts in modern developmental biology, such as germ layers (von Baer, 1828), the theory of natural selection (Darwin, 1859), and the Organizer (Spemann and Mangold, 1934). After World War II, especially after the demonstration of DNA as the genetic material and advancement in recombinant DNA technology, the focus of studies shifted to the cellular, molecular and genetic processes of development, the mechanisms of regulation, and the basis for developmental defects and diseases. In recent years, advancements in stem cell biology and gene editing technology ushered vertebrate embryology into a new era as scientists use the tools and paradigms of embryonic development to tackle diseases of all ages, bridging the embryo and the adult.

There is a vast body of research on vertebrate embryology, enough to fill a whole library. It is not the goal of this book to provide a comprehensive picture. Rather, I draw an extremely simplified sketch, a “tasting menu”, of current research topics. The book is organized into five sections. Section 1 illustrates a number of major research questions on the three developmental stages - cleavage, gastrulation, and organogenesis. Section 2 presents the frontiers in the study of genetic and epigenetic regulation: the role of genetic interactions, chromatin-based regulation, and non-coding RNAs. Section 3 describes the current research and application of stem cells. Section 4 introduces the role of genetic and environmental factors in developmental defects. Finally, Section 5 highlights the exciting new field of gene editing, using TALENs and CRISPR/Cas9 technologies as two examples.