This review discusses the drag coefficients over oceans and continents, focusing on aerodynamic roughness length (z₀) and friction velocity (u*). Observations over the past decade support Charnock's (1955) relation z₀ = αu*²/g with α = 0.0144 and a von Kármán constant of 0.41 ± 0.025. For practical purposes, the neutral drag coefficient (C_DN) varies with 10 m wind speed (V) in the range 4 < V < 21 m s⁻¹, either by a power law relation C_DN(10) × 10³ = 0.51V⁰.⁴⁶ or a linear form C_DN(10) × 10³ = 0.75 + 0.067V. Results from turbulence sensor experiments suggest that data scatter in C_DN(V) plots and systematic differences between data sets are mainly due to calibration uncertainties. The effects of fetch, wind duration, and unsteadiness remain obscured in this data scatter. Over land, vertical momentum transfer can be described using an effective roughness length or geostrophic drag coefficient. Low relief topography and low mountains require a geostrophic drag coefficient C_GN ≈ 3 × 10⁻³, while general land surfaces require C_GN ≈ 2 × 10⁻³, corresponding to C_DN(10) ≈ 10 × 10⁻³ and an effective aerodynamic roughness length of ≈ 0.2 m. These values satisfy the requirement of global angular momentum balance. For the sea, Charnock's relation suggests that z₀ depends only on u* and gravity, giving z₀g/u*² = constant (α). More recently, Kitaigorodskii and Zaslavskii considered transitional flow where fetch and wind duration might be important, such that z₀g/u*² = f(C₀/u*), where C₀ is the phase velocity of dominant waves. Observations of z₀ and C_DN(10) over the sea show that drag coefficients vary with wind speed, with values increasing with V. The variation of C_DN with V can be approximated by either a power law or linear relation. The value of α is found to be approximately 0.0144, close to values derived by Wu (1969) and Smith and Banke (1975). For land, vegetation and flat terrain have been studied, with z₀ values ranging from 0.01 to 1 m for extended land masses. The average z₀ is approximately 0.1 m, corresponding to C_DN(10) ≈ 7 × 10This review discusses the drag coefficients over oceans and continents, focusing on aerodynamic roughness length (z₀) and friction velocity (u*). Observations over the past decade support Charnock's (1955) relation z₀ = αu*²/g with α = 0.0144 and a von Kármán constant of 0.41 ± 0.025. For practical purposes, the neutral drag coefficient (C_DN) varies with 10 m wind speed (V) in the range 4 < V < 21 m s⁻¹, either by a power law relation C_DN(10) × 10³ = 0.51V⁰.⁴⁶ or a linear form C_DN(10) × 10³ = 0.75 + 0.067V. Results from turbulence sensor experiments suggest that data scatter in C_DN(V) plots and systematic differences between data sets are mainly due to calibration uncertainties. The effects of fetch, wind duration, and unsteadiness remain obscured in this data scatter. Over land, vertical momentum transfer can be described using an effective roughness length or geostrophic drag coefficient. Low relief topography and low mountains require a geostrophic drag coefficient C_GN ≈ 3 × 10⁻³, while general land surfaces require C_GN ≈ 2 × 10⁻³, corresponding to C_DN(10) ≈ 10 × 10⁻³ and an effective aerodynamic roughness length of ≈ 0.2 m. These values satisfy the requirement of global angular momentum balance. For the sea, Charnock's relation suggests that z₀ depends only on u* and gravity, giving z₀g/u*² = constant (α). More recently, Kitaigorodskii and Zaslavskii considered transitional flow where fetch and wind duration might be important, such that z₀g/u*² = f(C₀/u*), where C₀ is the phase velocity of dominant waves. Observations of z₀ and C_DN(10) over the sea show that drag coefficients vary with wind speed, with values increasing with V. The variation of C_DN with V can be approximated by either a power law or linear relation. The value of α is found to be approximately 0.0144, close to values derived by Wu (1969) and Smith and Banke (1975). For land, vegetation and flat terrain have been studied, with z₀ values ranging from 0.01 to 1 m for extended land masses. The average z₀ is approximately 0.1 m, corresponding to C_DN(10) ≈ 7 × 10