Stellar flares are sudden bursts of electromagnetic radiation from X-ray to radio wavelengths, occurring on most stars with outer convection zones. These flares are similar to solar flares but can be much more energetic. The origin of stellar flares is believed to be the conversion of magnetic field energy into atmospheric heating within a small region. This review covers recent decades of stellar flare research, including multi-wavelength observational results and the associated thermal and nonthermal processes in flaring stellar atmospheres. It also reviews static and hydrodynamic models, emphasizing recent progress in radiation-hydrodynamics and physical diagnostics in flare spectra. White-light stellar flares have gained renewed interest due to their impact on exoplanetary systems and the abundance of data from missions like *Kepler*. Despite significant progress, many aspects of stellar flares remain poorly understood, both empirically and theoretically. The review concludes with several key questions that are fundamental to advancing our understanding of these enigmatic phenomena.Stellar flares are sudden bursts of electromagnetic radiation from X-ray to radio wavelengths, occurring on most stars with outer convection zones. These flares are similar to solar flares but can be much more energetic. The origin of stellar flares is believed to be the conversion of magnetic field energy into atmospheric heating within a small region. This review covers recent decades of stellar flare research, including multi-wavelength observational results and the associated thermal and nonthermal processes in flaring stellar atmospheres. It also reviews static and hydrodynamic models, emphasizing recent progress in radiation-hydrodynamics and physical diagnostics in flare spectra. White-light stellar flares have gained renewed interest due to their impact on exoplanetary systems and the abundance of data from missions like *Kepler*. Despite significant progress, many aspects of stellar flares remain poorly understood, both empirically and theoretically. The review concludes with several key questions that are fundamental to advancing our understanding of these enigmatic phenomena.