A man pushes a massive block of ice through the streets of Mexico City until it melts to nothing. Five hundred volunteers walk over a huge sand dune in Lima, Peru, digging with spades and shifting the dune a few centimetres as they go. These are the works of the celebrated artist Francis Alÿs (born Belgium, 1959), and the subject of a major exhibition at Tate Modern.

Alÿs’s work starts with a simple action, either by him or others, which is then documented in a range of media. Alÿs explores subjects such as modernising programmes in Latin America and border zones in areas of conflict, often asking about the relevance of poetic acts in politicised situations. He has used video projection and film but also spreads his ideas through postcards. Painting and drawing remain central to his work too.

Alÿs moved to Mexico City in the mid 1980s at a time of political unrest, and lives there now. He began to make work which recorded everyday life, for example making slide works showing people sleeping on the streets or pushing mobile shopping stalls. Alÿs also makes works around the world. In The Green Line 2004, Alÿs walked along the 1948 armistice line between Israel and Palestine, trailing a line of green paint behind him, and provoking commentaries on the Israeli/Palestinian conflict.

This exhibition is his most comprehensive to date. It features many works unseen in Britain, such as When Faith Moves Mountains 2002 as well as premiering the major new work Tornado 2000–10.