Potato virus Y (PVY) is one of the most economically important plant pathogens. First described in the 1930s as a pathogen of potato, PVY infects a wide host range mainly within the Solanaceae and is distributed worldwide. This virus is transmitted by aphids in a non-persistent manner and has a single-stranded, positive-sense RNA genome of about 10 kb in length that encodes a large polyprotein cleaved into nine products and a recently described small open reading frame encoding the PIPO protein. Four host-dependent (tobacco, potato, tomato or pepper) classifications of PVY isolates have been established. This review will focus on PVY isolates that infect potato and that have historically been classified, according to their biological properties, into five strain groups. In the past 20 years, epidemiological studies have highlighted the emergence of additional distinct potato PVY isolates with increased virulence and/or aggressiveness. These isolates do not conform to the historical classification system. Biological, serological, and molecular comparisons of these new PVY isolates with historical isolates suggest that PVY is evolving both from mutations and recombination events. This paper reviews the main data resulting from a century of PVY evolution.