As the scaling of conventional planar CMOS is reaching its limits, multiple-gate CMOS structures will likely take up the baton. To facilitate circuit simulation in such advanced technologies, we have developed BSIM-MG: a versatile compact model for multi-gate MOSFETs. In this chapter separate formulations for common multi-gate and independent multi-gate MOSFETs are presented. The core I-V and C-V models are derived and agree well with TCAD simulations without using fitting parameters, reflecting the predictivity and scalability of the model. Physical effects such as volume inversion, short channel effects and quantum mechanical effects are included in the model. We verify BSIM-MG against triple-gate SOI FinFET experimental data. The model fits data very well across a wide range of biases, gate lengths and temperatures. It is also computationally efficient and suitable for simulating large circuits. Finally, several multi-gate circuit simulation examples are presented to demonstrate the use of the model.