his Brief Tech introduces an adaptation of the Mohr–Coulomb shear strength law for lunar conditions. It redefines cohesion as apparent cohesion (𝑐*), incorporates a stress-dependent friction angle (ϕ∗(p′)), and introduces the concept of cohesive length (ℓc). Apollo soil mechanics data are used to validate the framework, and worked examples with Blue Moon and Starship landers demonstrate the construction implications. The analysis shows why unmodified terrestrial soil mechanics underestimates lunar behaviour and why engineered ground preparation is essential for Artemis-era missions.