This chapter formulates the representative models and depicts the corresponding solutions for acoustic localization in the outdoor scenarios, where the sound signals are natural but not designed deliberately, such as gunfire and artillery firing. The focus is on the acoustic-energy localization, the time difference of arrival (TDOA)/frequency difference of arrival measurements for locating near-field moving sources, the direction estimation of far-field source via TDOA, the unified-field TDOA localization, and the bearing-based localization in three-dimensional space. The issue of sound speed variation caused by environmental condition is handled to avoid a considerable degradation of localization accuracy in the outdoor scenarios. The study of these techniques can help to choose a suitable solution to achieve a reasonable localization accuracy based on the available measurements.