This chapter delves into the critical issue of overfishing and its profound effects on marine biodiversity. Industrial fishing has escalated at an unprecedented rate over recent decades, driven by global demand and technological advancements, resulting in the depletion of numerous fish stocks and the destabilization of marine ecosystems. A major concern addressed is bycatch which is the unintentional capture of non-target species such as marine mammals, turtles and seabirds in which not only threatens these populations with decline but also upsets ecological balances. The destructive impact of certain fishing practices, notably bottom trawling, is highlighted for its role in devastating coral reef habitats, leading to the loss of essential breeding and feeding grounds for countless marine species. Through in-depth case studies, the chapter presents the consequences of tuna overfishing, which has pushed several species towards the brink of extinction, and examines the broad ecological repercussions of trawling on fragile seabeds, including habitat fragmentation and ecosystem degradation. The discussion integrates scientific perspectives and conservation voices, emphasizing the ripple effects of unsustainable fishing—ranging from diminished biodiversity and ecosystem services to food security concerns for human populations reliant on marine life. By illuminating these complex challenges, the chapter underscores the urgent need for sustainable fishing practices, strengthened regulatory frameworks and increased global cooperation to protect and restore marine biodiversity for future generations.