Oxidative stress arises from an imbalance between reactive oxygen species (ROS) production and antioxidant defense, which is implicated in many human diseases. However, it’s important to note that beyond their harmful effects, ROS also function as critical signaling molecules, orchestrating complex cellular responses. This dual role of ROS is a fundamental aspect of cell biology that plays a crucial role in the pathogenesis of numerous diseases, from cardiovascular disorders to neurodegenerative conditions and cancer. ROS are highly reactive molecules that can damage cellular components, including proteins, lipids, and DNA. In a healthy organism, there is a delicate balance between the production and detoxification of ROS. This chapter delves into the intricate signaling networks activated in response to oxidative stress. We explore the diverse array of ROS, including their generation mechanisms and biological roles. Key signaling pathways, such as MAPK, NF-κB, PI3K/Akt, NRF2, and so on, are discussed in detail, emphasizing their activation by ROS and subsequent transcriptional regulation of antioxidant enzymes, inflammatory mediators, and stress response proteins. Moreover, the chapter highlights the other cellular pathways, including apoptosis, autophagy, and inflammation.