<p>Contamination of soil and water by heavy metals and metalloids is one of the most persistent environmental problems of the modern industrial era. Because metals cannot be biologically degraded, remediation strategies must either remove or immobilise them. Conventional engineering methods&mdash;excavation, soil washing and chemical stabilisation&mdash;are effective but costly, energy-intensive and destructive to soil structure. Against this background, phytoremediation, the use of green plants to clean polluted media, has emerged as a low-cost, solar-driven and ecologically acceptable alternative. Central to this approach are <em>hyperaccumulator plants</em>&mdash;a remarkable group of species capable of concentrating metals in their above-ground tissues to levels hundreds or thousands of times greater than ordinary vegetation, without suffering toxicity. This review synthesises the concept, history and physiological basis of hyperaccumulation, surveys the global diversity of these plants (currently around 700 documented species), examines the molecular mechanisms of uptake, translocation and sequestration, and evaluates the principal phytoremediation strategies&mdash;phytoextraction, phytostabilisation, phytovolatilisation and rhizofiltration. Record-holding species such as <em>Pycnandra acuminata</em>, <em>Pteris vittata</em> and <em>Noccaea caerulescens</em> are discussed alongside emerging phytomining and agromining applications, before the advantages, limitations and future prospects of the technology are appraised.</p>