A Time-Turner is a magical device that allows a user to travel through time.
Use in Britain[]
The British Ministry of Magic kept a stock of Time-Turners stored in the Time Chamber of its Department of Mysteries. British Time-Turners resembled an hourglass set within several rotating rings, strung from brass chain.
In September of 1993, Hermione Granger was issued a Time-Turner by the Ministry in order for her to take more classes during the 1993-1994 schoolyear than would otherwise be possible. In June of 1994, Granger and Harry Potter used the Time-Turner to rescue the Hippogriff Buckbeak and wrongly-accused prisoner Sirius Black.
In June of 1996, the entired stock of Time-Turners kept by the Ministry of Magic was destroyed in a battle between the Order of the Phoenix and a group of Death Eaters.
Use in America[]
In September of 2009, Tabitha Speaks was issued a Time-Turner by the American Department of Magical Transportation in order to pick up students from across the country after the shutdown of the Wizardrail system. The more modern Time-Turner looks like "a very fine, gold pocket watch, with several extra dials."
At some point before November of 2009, Valeria White was issued a Time-Turner, most likely by the Academie de Magie, for use in her historical research of the beginnings of the American Wizarding Confederation. In November of 2009, White showed the Time-Turner to her half-sister, Alexandra Quick.