Briefing: What next for the fourth plinth?

It's one of Europe's most prestigious commissions. But the empty statue base in Trafalgar Square always attracts controversy

What is all this about the fourth plinth?

It's a stone statue base in the north-west corner of Trafalgar Square in London, which was originally supposed to support an equestrian statue of a military hero, as do plinths in the other corners. It has, however, remained empty since 1841. Since 1999 it has hosted a changing display of contemporary works. On Tuesday the six artists shortlisted for next year's commission, including Tracey Emin, Antony Gormley and Anish Kapoor, will exhibit models of their submissions at the National Gallery, a stone's throw from the plinth. Like all things to do with contemporary art, the fourth plinth project has not been without controversy.

Controversial? You don't say

First, the programme ground to a halt in 2001. Plans to erect a permanent statue of Nelson Mandela were then thwarted by Westminster City Council. In 2003 Ken Livingstone, the Mayor of London, reintroduced the fourth plinth project, taking over from the Royal Society of Arts. The first work, Alison Lapper Pregnant, Marc Quinn's 12ft marble statue of the naked, then-pregnant artist who has no arms, was described as "horrible" by one critic, although on purely artistic grounds. It was in place for two years, instead of the intended 18 months, as the next work, Model for a Hotel by Thomas Schutte, was delivered several months late. This multi-coloured 24-storey glass hotel was originally called Hotel for the Birds, possibly for pigeons which have since been banished from the square.

Who decides?

The Fourth Plinth Commissioning Group, which is chaired by Sandy Nairne, the director of the National Portrait Gallery. It includes the broadcaster Jon Snow and the Turner Prize-winning ceramicist Grayson Perry. They do, however, take into account comments made by the public during the shortlist exhibition.

So, what's next?

For an artist it is one of most prestigious commissions in Europe. There are few other places quite so public and famous. It is also a challenge. With a potential audience of millions the work has to hold its own against Nelson's Column and the great work in the National Gallery. The models for the next commission are being kept under wraps. Emin, however, is said to have proposed a clan of meerkats, while the husband and wife team Bob and Roberta Smith are renowned for painting slogans on bits of reclaimed wood.