By the process of organogenesis, the internal organs and specific body parts (such as limbs) are formed during the development of an organism. Organogenesis involves the coordination of multiple developmental processes such as embryonic induction, pattern formation, morphogenesis, cell proliferation and differentiation.
In humans, internal organs begin to develop within 3 to 8 weeks after fertilization. The cells of each of the three germ layers undergo differentiation from less specialised cells to more specialised cells. The internal organs are formed by folding, splitting and condensation of the germ layers. The germ layers of the embryo differentiate and specialise to form the various organs of the body.
In plants organogenesis occurs continuously and stops only when the plant dies. Plant organogenesis can be induced in tissue culture and to regenerate plants.