Phase diagrams are the foundation in performing basic materials research in such fields as solidification, crystal growth, joining, phase transformation, etc and serve as a road map for materials design and process optimization since it is the starting point in the manipulation of processing variables to achieve the desired microstructures. Traditionally phase diagrams were determined primarily by meticulous and costly experimentation. While this approach has been both feasible and necessary for determining phase equilibria of binaries and those of ternaries over limited compositional regions, it is nearly impossible to use such an approach for the determination of phase diagrams of ternary and higher order systems over wide ranges of compositions and temperatures. Yet, most if not all real alloys are multicomponent, often more than 10. In this presentation, we will show that significant progress has been made in the use of the phenomenological or Calphad route to calculate phase diagrams of multicomponent alloys for industrial applications. The essence of this approach is to obtain the parameters of thermodynamic models for the Gibbs energies of the constituent phases in the lower order systems, binaries and ternaries, in terms of known thermodynamic and phase equilibrium data. We can then obtain the Gibbs energies of multicomponent alloy phases from those of the lower order systems via an extrapolation method. These Gibbs energy values enable us to calculate reliable multicomponent phase diagrams in many instances. Experimental work is then only required for the purpose of confirmation instead of determination of the whole diagrams. We will present several concrete examples to show that calculated multicomponent phase diagrams have been utilized to identify multicomponent alloys for bulk glass formation, to minimize cracks in aluminum alloy welds, to predict microsegregation in castings, and to possibly replace experimentation to certify alloys for commercialization.