The Isle of Man TT or Tourist Trophy races are an annual motorcycle sport event run on the Isle of Man in May/June of most years since its inaugural race in 1907. The event is often called one of the most dangerous racing events in the world.

The Isle of Man TT is run in a time-trial format on public roads closed to the public by an Act of Tynwald (the parliament of the Isle of Man). The event consists of one week of practice sessions followed by one week of racing. It has been a tradition, perhaps started by racing competitors in the early 1920s, for spectators to tour the Snaefell Mountain Course on motorcycles during the Isle of Man TT on "Mad Sunday", an informal and unofficial sanctioned event held on the Sunday between 'Practice Week' and 'Race Week'.

The first Isle of Man TT race was held on Tuesday 28 May 1907 and was called the International Auto-Cycle Tourist Trophy. From 1911 the Isle of Man TT transferred to the much longer Snaefell Mountain Course of 37.40 miles (60.19 km) (current length 37.73 miles (60.72 km)). Its elevation goes from sea-level to 1,300 feet.

It is still regarded in popular culture as the most dangerous motorsport event in the world, with the New York Times stating that the number of deaths has risen "to 146 since it was first run in 1907; if one includes fatal accidents occurring during the Manx Grand Prix, the amateur races held later in the summer on the same Snaefell Mountain Course, the figure rises above 250".

More Info: en.wikipedia.org