A 99-year lease was, under historic common law, the longest possible term of a lease of real property. It is no longer the law in most common law jurisdictions today, yet 99-year leases continue to be common as a matter of business practice and conventional wisdom.
Under the traditional American common law doctrine, the 99-year term was not literal, but merely an arbitrary time span beyond the life expectancy of any possible lessee (user) or lessor (owner).
William Blackstone (1723–1780, of Commentaries on the Laws of England fame) states that a lease was formerly limited to 40 years, although much longer leases (for 300 years, or 1000 years) were in use by the time of Edward III. The 40-year limit was based on the unreliable text "The Mirror of Justices" (book 2, chapter 27).
In the law of several US states, a 99-year lease will always be the longest possible contract for realty by statute, but many states have enacted shorter terms and some allow infinite terms.
Due to the influence of the ideas of Henry George at the time the Australian Capital Territory (ACT) was established in the early 20th century, all land in the ACT is held under 99-year leases, the first of which will expire in 2023.
- Boston Museum of Science
- Ontario Highway 407 - leased by the provincial government under Mike Harris for C$3.1 billion.
- Panama Canal
- British Hong Kong and Convention for the Extension of Hong Kong Territory resulted in the 99-year lease of Kowloon, New Territories to Britain in 1898
- Magampura Mahinda Rajapaksa Port - Sri Lanka to China
- Mortgage News Daily web site article on a 99-year lease. Accessed 20 February 2008.
- Cecil Adams, Why are leases made for 99-year terms?, 22 July 1977, found at The Straight Dope article on 99-year lease. Accessed 20 February 2008.
- William Blackstone (1753), Commentaries on the Laws of England, Book 2, Chapter IX "Of estates less than freehold"
- Taylor, Gordon (4 July 2016). "Can people own land in the ACT?". ABC News. Australian Broadcasting Corporation. Retrieved 24 July 2018.