Being a crucial part of the earth’s surface, trees affect boundary layer dynamics. As a viscous medium allowing flow penetration, a tree canopy interacts directly with air flow, exerting drag as described by the surface roughness parameters, and exchanging fluxes of heat, water, and gases such as CO2, O2, and volatile organic compounds (VOCs). Trees affect the energy budget through changing the reflectivity of the surface (described by the albedo parameter) and the ratio of surface energy that contributed to heat flux vs. vaporization of water (known as the Bowen ratio). The complex structure of tree canopies represents a challenge for modeling their effects on drag and surface fluxes. Depending on the modeling need and the desired resolution, a canopy can be modeled simply as a coarse flat surface that acts as a surface boundary condition of the atmospheric dynamics, or it can be represented by its vertical structure characteristics to some degree of simplification. A canopy can even be modeled three-dimensionally to show its structure and its direct interactions with the atmosphere at high resolution. Understanding air–canopy interactions is crucial for weather and climate modeling and improving our modeling capabilities of vegetation–air interaction is an active research avenue.