Resonance Raman spectroscopy is a powerful tool for probing electron–phonon coupling, phonon momentum distributions, and stacking-related spectral features in InSe. Based on first-principles calculations, we systematically investigate the single-resonance Raman (SRR) and double-resonance Raman (DRR) scattering behaviors of monolayer InSe and bilayer $\beta$- and $\epsilon$-phase InSe. For monolayer InSe, the SRR response is dominated by the hole-scattering pathway (h-path), while the out-of-plane, out-of-phase Se–In vibration near $235{\mathrm{cm}}^{-1}$ $\left({\mathrm{A}}_1^{\prime 2}\right)$ exhibits the strongest resonance enhancement. The principal DRR peaks mainly originate from near-$\mathrm{\Gamma }$ intravalley overtone scattering of the in-plane Se–In relative-vibration branch $\left({\mathrm{E}}^{\prime 2}\right)$ and exhibit weak excitation-energy dispersion, while the mixed electron–hole scattering pathways (eh- and he-paths) also make appreciable contributions. Under $4.66\mathrm{eV}$ excitation, the high-frequency broad band evolves into two components, associated with additional strong resonant optical-transition channels along the $\mathrm{\Sigma }\text{–}\mathrm{M}$ direction. For bilayer InSe, the resonance enhancement of low-frequency interlayer phonon modes in the SRR spectra provides fingerprints of the layer number. In the DRR spectra, the nearly excitation-energy-independent lower-frequency principal peak $\left({\mathrm{P}}_1\right)$ is blue-shifted by approximately $9{\mathrm{cm}}^{-1}$ relative to monolayer InSe and can serve as a layer-number indicator, whereas the broad higher-frequency peak $\left({\mathrm{P}}_3\right)$ is more sensitive to stacking order and excitation energy, with the $\epsilon$ phase expected to exhibit a more pronounced excitation-energy-induced shift than the $\beta$ phase. These results clarify the microscopic origin of resonance Raman scattering in InSe and provide a theoretical basis for characterizing its layer number, interlayer vibrations, and stacking structures.

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• Bilayer films
• Monolayer films
• Density functional calculations
• Raman spectroscopy