The present report aims to review the most recent scientific data and studies on Marek's disease virus (MDV) in poultry. The disease is caused by Gallid alphaherpesvirus 2 (MDV-1), a herpesvirus that induces T-cell lymphomas, nerve enlargement, and various neurological and visceral lesions in chickens. Despite widespread vaccination, Marek’s disease (MD) still leads to severe economic losses due to reduced productivity, high mortality, and costly control measures. Three serotypes of the virus are known: MDV-1, which is oncogenic; and MDV-2 and MDV-3, which are non-pathogenic and used as vaccine strains. MDV-1 isolates are classified by virulence as mMDV, vMDV, vvMDV, and vv+MDV. Recent Asian studies have identified highly virulent field strains with mutations in the Meq oncogene, suggesting viral evolution and vaccine escape. Transmission occurs mainly through inhalation of feather dust from infected birds, as the virus is not vertically transmitted. It remains highly stable in the environment, persisting in poultry houses for long periods. Lesions may appear in the nerves, liver, spleen, kidneys, and eyes, often causing paralysis or “grey eye.” Diagnosis combines clinical signs, pathology, and molecular tests such as PCR targeting Meq, gL, and ICP4, along with immunohistochemistry. Although vaccination has greatly reduced disease impact, the continuous evolution of virulent strains threatens vaccine efficacy and highlights the need for improved prevention strategies.