Solving the grand challenge problems in many areas such as development of new materials and sources of energy, development of new medicines and improved health care, strategies for disaster prevention and mitigation, and for scientific research including the origins of matter and the universe, requires Teraflops performance for more than a thousand hours at a time. In future, we will need Petaflops or Exaflops level of computation power. To achieve this level of performance, we need massively parallel computer (MPC) systems with millions of nodes. k-ary n-cube is a node and edge symmetric regular network, which has an ability to exploit locality exhibited by many parallel applications. However, high wiring complexity make it insatiable for a network consisting of millions of nodes. Hierarchical interconnection network (HIN) is an efficient way to interconnect the future MPC systems. k-ary n-cube based HIN is a plausible alternative way because each level of hierarchy have toroidal interconnections. Several k-ary n-cube based HINs and their routing algorithm, static network performance, and dynamic communication performance has been extensively studied in this book.