The chapter discusses recent advancements in the degradation and toxicological studies of polymeric nanocomposites, which have gained popularity due to their superior mechanical, thermal, and barrier properties. As the use of these materials increases, understanding their environmental and biological impacts becomes crucial. The degradation mechanisms of polymeric nanocomposites are determined by factors such as the polymer type, the nature and concentration of nanoparticles, and environmental conditions like temperature, UV exposure, and humidity. During degradation, the release of nanoparticles may pose potential risks to human health and the environment, necessitating comprehensive toxicological evaluations. Research indicates that while some nanocomposites degrade into non-toxic byproducts, others can release harmful nanoparticles, leading to cytotoxicity, genotoxicity, and environmental persistence. Polymer nanocomposites containing engineered nanomaterials (ENMs) are increasingly used in various applications, but concerns have been raised about the potential release of these nanomaterials and their environmental impact. Studies have shown that ENMs can be released from nanocomposites through matrix degradation mechanisms, including photodegradation, thermal decomposition, mechanical wear, and hydrolysis. UV radiation, in particular, can cause rapid photodegradation of polymer matrices, leading to increased concentrations of nanofillers at the composite surface and potential release. The nature of the nanofiller and polymer matrix, as well as environmental exposure conditions, influence the degradation and release processes. Recovery of nanomaterials from degraded composites has been achieved using techniques such as dissolution and calcination. While free nanofillers may pose toxicological risks, some studies suggest that embedding them in polymer matrices could reduce their toxicity. Advanced analytical techniques, such as spectroscopy, electron microscopy, and in vitro/in vivo assays, are essential for characterizing degradation products and evaluating their toxicological profiles. These findings highlight the importance of designing nanocomposites with controlled degradation rates and minimal toxicological impact, balancing their functional advantages with considerations for environmental and health safety.