There is now a considerable body of experimental evidence to indicate that in a volumediffusion controlled interaction the Kirkendall plane need not be unique. The Kirkendall plane can microstructurally be stable as well as unstable (it does not exist!). Under predictable circumstances, it can also bifurcate and even trifurcate. This can be rationalised in terms of Kirkendall velocity construction as well as from a purely chemical point of view considering diffusion-controlled interactions at the interphase interfaces. The physico-chemical approach is also used to explain significance of the Kirkendall effect in the morphogenesis of interdiffusion systems.