This chapter provides details about how to model and simulate one-way and two-way fluid-structure interaction (FSI) completely within a Fluent session. This is referred to as "intrinsic FSI", as all of the structural calculations are performed by Fluent; note that you can also use extrinsic solvers for FSI problems, incorporating the structural data into your Fluent fluid simulation through mapping or system coupling, as described in Mapping Data for Fluid-Structure Interaction (FSI) Applications and Performing System Coupling Simulations Using Fluent, respectively. The theoretical aspects of intrinsic FSI calculations are presented in The Structural Model for Intrinsic Fluid-Structure Interaction (FSI) in the Theory Guide. The following sections provide details on running intrinsic FSI simulations: