This chapter will investigate the contact interaction physics and contact properties implemented with both Abaqus standard and explicit solvers. Contact definition is a source of high nonlinearity in FEA model and therefore, a good understanding regarding how to make a correct representation of physics in the model with the proper parameters will help to avoid numerical difficulties or an unconverged solution. Contact interactions are less complex to understand but more difficult to use because of the multiple combinations of settings to make a proper contact definition. This is why the sections in this chapter will take a closer look at contact generalities, contact and friction, hard and soft contact, and then different procedures used to fix certain troubleshooting issues related to contact. A series of examples will also be given to have a better overview of some option setting consequences.