Emerging environmental contaminants (EECs) such as personal care products, pharmaceuticals, microplastics, heavy metals, and industrial chemicals are causing problem to ecosystem and mankind due to their persistence, low degradation, and low regulatory conditions. The complicated biological effects of these pollutants are frequently failed by conventional chemical detecting methods. Bio-indicators, organisms that imitate the health of their surrounding environment, offer a sensitive, integrative, and cost-effective alternative for detecting these contaminants. In this chapter we will explore the classification of EECs, the concept and types of bio-indicators, advances in biomonitoring systems and mechanisms of biological response. By referring case studies and recent advancements, it shows how bio-indicators are progressively being implemented into environmental policy and monitoring frameworks. For the task such as environmental variability, standardization, and the need for more reliable analytical tools. It summarizes by looking to future possibilities, considering how omics technologies and artificial intelligence could improve the use and effectiveness of bio-indicators.