Heavy metals (HMs) carry a prominent threat to human beings and the ecosystem considering their prevalence, toxicity, and capacity to bioaccumulate in organisms. This chapter sheds light on the various aspects of HM sources, routes of exposure, and associated health impacts. HMs originate naturally from natural calamities like volcanic eruptions, weathering, and soil resuspensions, anthropogenic activities like urbanization, industrialization, mining, and agricultural events have a significant contribution to the elevating prevalence of these HMs which are present in various environmental ecosystems from where they find their routes to enter in living organisms. These HMs tend to enter through inhalation, ingestion, or dermal contact, as they are the significant pathways followed by occupational and consumer exposures. The chapter particularly delves into health toxicities caused by eight HMs: lead, mercury, nickel, cadmium, arsenic, chromium, manganese, and cobalt. These HMs are marked for their toxic and carcinogenic natures with no known biological functions, causing detrimental effects like neurological, reproductive, and digestive system alterations in humans. Furthermore, these metals pose a threat to plants by generating reactive oxygen species, decreasing photosynthesis, reducing seed germination, slowing growth, and causing histological and physiological damage in animals. This chapter also emphasizes various diagnostic techniques and tools to determine HMs. Finally, it highlights the need for strict laws and guidelines to overcome the impacts of HMs and safeguard human health and the ecosystem.