In 1975 the voting system of 12, 10, 8 etc to 1 point was introduced.

As the number of countries wishing to participate grew, 1993 and 1996 saw elimination rounds (see 1993 and 1996).
The losing countries could NOT vote in the final.

In 2004 this rule changed with the introduction of televised semi-finals.
Originally the 'Big Five' (Germany, France, United Kingdom, Spain, Italy) plus the Top Ten of the previous year were pre-qualified for the final, but in 2008 this was reduced to just the Big Five plus the host country.
The Big Five are always qualified for the final and will never have to take part in the semi finals.

In the final, all countries, including the losing semi-finalists, can vote.