Bly is a surname. Notable people with the surname include:
- Adam Bly (born 1981), Canadian scientist and entrepreneur
- Beldon Bly (1914–2006), American teacher and politician
- Billy Bly (1920–1982), English professional football goalkeeper
- Carol Bly (1930-2007), short story writer
- David Bly (born 1952), American politician
- Dré Bly (born 1977), American football coach and player
- John Bly (born 1939), English antiques specialist
- Mark Bly (born 1949), American dramaturge, educator, and author
- Mary Bly (born 1962), author who publishes under the name Eloisa James
- Nellie Bly, pen name of Elizabeth Cochrane Seaman (1864–1922), American journalist, author, industrialist, and charity worker
- Robert Bly (1926–2021), author of Iron John (book)
- Robert W. Bly (born 1957), American writer
- Stephen Bly (1944–2011), American author and politician
- Terry Bly (1935–2009), footballer who played for Norwich City and Peterborough United