The memristor has quite a reputation as a missing circuit element. It is a powerful candidate for next-generation applications after being first implemented in HP's laboratories. At this point, mathematical models were needed for the analysis of the memristor, and a lot of studies were done on this subject. In this chapter, mathematical modeling and simulations of the memristor device have been emphasized. Firstly, linear drift and nonlinear drift models have been described on the basic HP model. The window functions used in the nonlinear drift model have been widely examined. Different from HP model, the Simmons tunnel barrier and the threshold adaptive memristor model (TEAM) have been also mentioned. As a result, the most widely used modeling techniques have been described in detail.