Insects are among the most diverse and abundant organisms on Earth and play essential roles in ecosystem functioning. Due to their sensitivity to environmental changes, short life cycles, and wide ecological distribution, insects are increasingly recognized as effective bioindicators of environmental health. Changes in insect diversity, abundance, behavior, and community composition reflect alterations in habitat quality, pollution levels, climate change, and land-use practices. This review examines the role of insects as bioindicators, highlights major insect groups used in environmental monitoring, discusses methodologies and applications, and outlines current challenges and future perspectives in sustainable environmental assessment.