Gravitational waves (GWs) are a unique probe of the early universe, as they can detect primordial events that occurred during inflation. This article reviews the prospects for detecting a stochastic GW background and the sources that could generate such a background. The detection of GW backgrounds relies on various strategies, including pulsar timing arrays, astrometry, and interferometers. The article also delves into three major primordial events that can produce GW backgrounds: cosmic phase transitions, topological defects, and scalar-induced GWs. Each section discusses the theoretical framework, modeling, and potential observations of these events. Additionally, the article explores other significant sources of GW backgrounds, such as inflation and reheating. The detection of GW backgrounds offers a window into the early universe, providing insights into physics beyond the Standard Model, particularly at high energy scales.Gravitational waves (GWs) are a unique probe of the early universe, as they can detect primordial events that occurred during inflation. This article reviews the prospects for detecting a stochastic GW background and the sources that could generate such a background. The detection of GW backgrounds relies on various strategies, including pulsar timing arrays, astrometry, and interferometers. The article also delves into three major primordial events that can produce GW backgrounds: cosmic phase transitions, topological defects, and scalar-induced GWs. Each section discusses the theoretical framework, modeling, and potential observations of these events. Additionally, the article explores other significant sources of GW backgrounds, such as inflation and reheating. The detection of GW backgrounds offers a window into the early universe, providing insights into physics beyond the Standard Model, particularly at high energy scales.