This chapter will examine the cell and molecular biology of the embryogenic development of somatic cells of angiosperms and gymnosperms, or the phenomenon of somatic embryogenesis. Embryogenic development of somatic cells can be contrasted to the rigorously programmed development of the embryo from the zygote (zygotic embryogenesis) insofar as virtually any somatic cell of the plant body can, under certain experimental conditions, behave like a zygote and faithfully replay a developmental program leading to the production of embryolike structures while remaining innocent of sex. Thus, somatic embryogenesis provides the most clear-cut demonstration of the dictum that all plant cells except those that have undergone irreversible differentiation are totipotent and retain the developmental potential to proliferate into an adult plant. Compared to the limited number of embryos arising from gametic fusion and the difficulty of extracting them from the confines of the ovule, the enormous number of somatic cells potentially capable of embryogenic development ensures the availability of an equally staggering number of embryolike structures by simple experimental manipulations. Despite the fact that zygotic embryos and embryolike structures formed from somatic cells are identical in appearance and possess the same morphogenetic potential, to emphasize the divergent pathways through which they have evolved, the term “embryoid” is generally used to refer to the latter.