This paper investigates Scalar-Induced Gravitational Waves (SIGWs), a type of primordial gravitational wave signal generated by second-order scalar fluctuations in the early universe. These waves form a stochastic gravitational wave background (SGWB) that can be detected by future gravitational wave detectors like LISA. The amplitude and frequency shape of the SGWB depend on the statistical properties of the primordial scalar density perturbations, particularly their non-Gaussianity. The study considers all relevant non-Gaussian contributions up to fifth order in the scalar seeds, without assuming any hierarchy among the non-Gaussian parameters. The authors derive the gravitational wave energy density ΩGW(f) and perform a Fisher matrix analysis to assess the accuracy with which non-Gaussianity can be constrained by LISA. They find that LISA could measure the amplitude, width, and peak of the SGWB spectrum with an accuracy of up to 10⁻⁴, while non-Gaussianity could be measured up to 10⁻³. The results also have implications for the formation of Primordial Black Holes (PBHs), as non-Gaussianity affects the distribution of fluctuations that could lead to PBH formation. The study shows that SIGWs can be used to constrain the parameter space of models that generate PBHs, providing a complementary method to study non-Gaussianity. The paper also discusses the connection between SIGWs and PBH abundance, highlighting the importance of considering all non-Gaussian contributions for accurate predictions. The results are compared with the sensitivity of the LISA detector, and the paper concludes with a summary of the main findings and their implications for future gravitational wave observations.This paper investigates Scalar-Induced Gravitational Waves (SIGWs), a type of primordial gravitational wave signal generated by second-order scalar fluctuations in the early universe. These waves form a stochastic gravitational wave background (SGWB) that can be detected by future gravitational wave detectors like LISA. The amplitude and frequency shape of the SGWB depend on the statistical properties of the primordial scalar density perturbations, particularly their non-Gaussianity. The study considers all relevant non-Gaussian contributions up to fifth order in the scalar seeds, without assuming any hierarchy among the non-Gaussian parameters. The authors derive the gravitational wave energy density ΩGW(f) and perform a Fisher matrix analysis to assess the accuracy with which non-Gaussianity can be constrained by LISA. They find that LISA could measure the amplitude, width, and peak of the SGWB spectrum with an accuracy of up to 10⁻⁴, while non-Gaussianity could be measured up to 10⁻³. The results also have implications for the formation of Primordial Black Holes (PBHs), as non-Gaussianity affects the distribution of fluctuations that could lead to PBH formation. The study shows that SIGWs can be used to constrain the parameter space of models that generate PBHs, providing a complementary method to study non-Gaussianity. The paper also discusses the connection between SIGWs and PBH abundance, highlighting the importance of considering all non-Gaussian contributions for accurate predictions. The results are compared with the sensitivity of the LISA detector, and the paper concludes with a summary of the main findings and their implications for future gravitational wave observations.