This thesis discusses the concepts of a newly-developed mechanical network element, called Inerter. This passive element was invented in 2001 from the imperfect analogy between mechanical and electrical networks, and was first applied to car suspension system. In this thesis, we extended the ideal to train suspension systems by combining Inerter with the traditional suspension systems. Both of the transfer function and state-space methods were used to build the quarter, two wheel, four wheel, and full train models. From various performance index analyses, it was shown that Inerter is beneficial to train performance. Finally, we discussed lateral stability and critical speed for the full train system to show the potential improvement of safety by Inerter.