[en] We report second- and third-harmonic generation in monolayer MoS₂ as a tool for imaging and accurately characterizing the material’s nonlinear optical properties under 1560 nm excitation. Using a surface nonlinear optics treatment, we derive expressions relating experimental measurements to second- and third-order nonlinear sheet susceptibility magnitudes, obtaining values of $|{\mathrm{\chi <!--\; ??\; -->}}_{\mathrm{s}}^{(2)}|=2.0\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->20}$ m² V⁻¹ and, for the first time for monolayer MoS₂, $|{\mathrm{\chi <!--\; ??\; -->}}_{\mathrm{s}}^{(3)}|=1.7\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->28}$ m³ V⁻². These sheet susceptibilities correspond to effective bulk nonlinear susceptibility values of $|{\mathrm{\chi <!--\; ??\; -->}}_{\mathrm{b}}^{(2)}|=2.9\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->11}$ m V⁻¹ and $|{\mathrm{\chi <!--\; ??\; -->}}_{\mathrm{b}}^{(3)}|=2.4\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->19}$ m² V⁻², accounting for the sheet thickness. Experimental comparisons between MoS₂ and graphene are also performed, demonstrating ∼3.4 times stronger third-order sheet nonlinearity in monolayer MoS₂, highlighting the material’s potential for nonlinear photonics in the telecommunications C band. (letter)