Nanoelectromechanical systems (NEMS) are nano-to-micrometer scale mechanical resonators coupled to electronic devices of similar dimensions. These systems show promise for fast, ultrasensitive force microscopy and for deepening our understanding of how classical dynamics arises from quantum dynamics. This article begins with a survey of NEMS and then describes certain aspects of their classical dynamics. In particular, it is shown that for weak coupling, the action of the electronic device on the mechanical resonator can be effectively that of a thermal bath, despite the device being a driven, far-from-equilibrium system. The article also discusses various representative NEMS devices, including the mechanically compliant tunneling electrode, the quantum point contact displacement detector, and the single electron transistor displacement detector. It explores the coupled dynamics of the SET-mechanical resonator system, focusing on the effective equilibrium description in the weak-coupling regime. The master equations for the coupled system are derived, and the steady-state behavior is analyzed. The results suggest that the SET appears to the mechanical resonator as a thermal bath, provided there is a wide separation in the dynamics timescales of the resonator and the SET.Nanoelectromechanical systems (NEMS) are nano-to-micrometer scale mechanical resonators coupled to electronic devices of similar dimensions. These systems show promise for fast, ultrasensitive force microscopy and for deepening our understanding of how classical dynamics arises from quantum dynamics. This article begins with a survey of NEMS and then describes certain aspects of their classical dynamics. In particular, it is shown that for weak coupling, the action of the electronic device on the mechanical resonator can be effectively that of a thermal bath, despite the device being a driven, far-from-equilibrium system. The article also discusses various representative NEMS devices, including the mechanically compliant tunneling electrode, the quantum point contact displacement detector, and the single electron transistor displacement detector. It explores the coupled dynamics of the SET-mechanical resonator system, focusing on the effective equilibrium description in the weak-coupling regime. The master equations for the coupled system are derived, and the steady-state behavior is analyzed. The results suggest that the SET appears to the mechanical resonator as a thermal bath, provided there is a wide separation in the dynamics timescales of the resonator and the SET.