This tutorial review provides an overview of theoretical methods for predicting and understanding the optical response of gold nanoparticles. It discusses the effects of retardation in large particles and non-locality in small particles, and emphasizes the relevance of near-field spectra in surface-enhanced Raman spectroscopy and electron energy-loss spectroscopy. The review covers analytical models and numerical methods, including the boundary element method (BEM), discrete-dipole approximation (DDA), and finite difference in the time domain method (FDTD). It also highlights the importance of particle shape, size, and dielectric environment on the optical properties of gold nanoparticles. The review concludes with a critical comparison of computational methods based on their speed, storage demand, versatility, and suitability for different particle geometries and dielectric functions.This tutorial review provides an overview of theoretical methods for predicting and understanding the optical response of gold nanoparticles. It discusses the effects of retardation in large particles and non-locality in small particles, and emphasizes the relevance of near-field spectra in surface-enhanced Raman spectroscopy and electron energy-loss spectroscopy. The review covers analytical models and numerical methods, including the boundary element method (BEM), discrete-dipole approximation (DDA), and finite difference in the time domain method (FDTD). It also highlights the importance of particle shape, size, and dielectric environment on the optical properties of gold nanoparticles. The review concludes with a critical comparison of computational methods based on their speed, storage demand, versatility, and suitability for different particle geometries and dielectric functions.