This review by Nicolas G. Hadjiconstantinou, from the Department of Mechanical Engineering at the Massachusetts Institute of Technology, focuses on the molecular mechanics of slip flow at the solid-liquid interface. Slip flow occurs when the tangential velocity of a fluid is not equal to the velocity of the solid it contacts, typically due to the inhomogeneity introduced by the solid boundary. This review aims to summarize our current understanding of slip flow at the atomistic level in dilute gases and dense liquids, emphasizing the similarities and differences between slip in gases and liquids, characterization and measurement of slip using molecular simulation methods, and open questions requiring further investigation. The introduction highlights the importance of slip flow in extending traditional Navier-Stokes-based hydrodynamic models to smaller scales and confined geometries. Slip flow can significantly enhance flow rates, especially in nanotubes, and is crucial for understanding both scientific and practical aspects. The review is divided into two main sections: slip in dilute gases and slip in dense liquids. For dilute gases, the focus is on the kinetic theory treatment, including the Boltzmann equation and the Maxwell boundary condition. The discussion covers first-order and second-order asymptotic analyses, providing detailed slip relations and their implications. For dense liquids, the review discusses molecular simulation methods, such as nonequilibrium and equilibrium approaches, and slip models, including the impact of liquid layering at the solid-liquid interface. Key findings include the robustness of slip-flow theory beyond its nominal limits, the importance of the hydrodynamic wall location in equilibrium slip measurements, and the need for more accurate computational methods to predict slip coefficients in general solid-liquid systems. The review also highlights the challenges and limitations in characterizing slip in dense liquids, particularly due to the complex intermolecular interactions.This review by Nicolas G. Hadjiconstantinou, from the Department of Mechanical Engineering at the Massachusetts Institute of Technology, focuses on the molecular mechanics of slip flow at the solid-liquid interface. Slip flow occurs when the tangential velocity of a fluid is not equal to the velocity of the solid it contacts, typically due to the inhomogeneity introduced by the solid boundary. This review aims to summarize our current understanding of slip flow at the atomistic level in dilute gases and dense liquids, emphasizing the similarities and differences between slip in gases and liquids, characterization and measurement of slip using molecular simulation methods, and open questions requiring further investigation. The introduction highlights the importance of slip flow in extending traditional Navier-Stokes-based hydrodynamic models to smaller scales and confined geometries. Slip flow can significantly enhance flow rates, especially in nanotubes, and is crucial for understanding both scientific and practical aspects. The review is divided into two main sections: slip in dilute gases and slip in dense liquids. For dilute gases, the focus is on the kinetic theory treatment, including the Boltzmann equation and the Maxwell boundary condition. The discussion covers first-order and second-order asymptotic analyses, providing detailed slip relations and their implications. For dense liquids, the review discusses molecular simulation methods, such as nonequilibrium and equilibrium approaches, and slip models, including the impact of liquid layering at the solid-liquid interface. Key findings include the robustness of slip-flow theory beyond its nominal limits, the importance of the hydrodynamic wall location in equilibrium slip measurements, and the need for more accurate computational methods to predict slip coefficients in general solid-liquid systems. The review also highlights the challenges and limitations in characterizing slip in dense liquids, particularly due to the complex intermolecular interactions.