Design basis is basis for design for any project. it has to be developed in the starting of the project. This series talk about design basis and its importance. All the components have been covered and explained in detail. For any project process discipline plays an important role for designing. Along with the design basis, all the process interface inputs and outputs have been discussed in detail. all process inputs which are required at the starting of the project eg Fluid list, line list, PIDs and Pfds are discussed in detail.