Tate Modern now has its wonderful long-time-coming extension - although extension does not seem quite the right word for the new £260m Herzog & de Meuron building when the same architects first transformed the old Bankside power station into a museum for a 'mere' £134m back in 2000. What Tate gets for its money is 60 per cent more gallery space: that's a lot of new rooms to fill. Alongside Tate's mission statement to include more global contemporary works, it also intends to show more photography and video art. The old argument 'Is photography art?' is pretty much over, and those new exhibition spaces are ready.

Not that Tate has been waiting. Earlier this year, for example, it put on Performing for the Camera, an exhibition of the blurred lines between photography and performance art. And recently opened is an exhibition of the work of Mona Hatoum, the London-based Palestinian video and performance artist whose work is designed to elicit strong responses.

Indeed, eliciting responses from the viewer is one of the hallmarks of the current crop of photographers and video artists; for them, a passive response or a quiet contemplation of beauty is not enough. Hatoum's work, for example, deals with such big and non-neutral issues as politics, gender and the body. A piece such as her 1988 video 'Measures of Distance' combined not just these themes but added others, such as displacement and family. It showed photographs of Hatoum's mother showering, the images overlaid with the letters she wrote to her daughter in London. It is a work of complexity and emotional intensity.

An artist such as the German Wolfgang Tillmans uses photographs in a different way. 'I take pictures in order to see the world' he has said, and he made his name by photographing everything he saw - from friends embracing to aeroplanes flying overhead - in a compulsive but seemingly random way. He has moved on to explore the medium itself - using clusters of photographs in galleries as elements in installations that include laserjet prints as well as more traditionally framed 'high art' photographs.

A more traditional approach is practised by Simon Norfolk, who has subsumed his early career as a photojournalist into his current one as a landscape photographer. His pictures are carefully composed and lit, but the landscapes they show are far from picturesque, although they can be that, too. He seeks out the strange beauty found in a ravaged country such as Afghanistan and contrasts nature's fecundity with man's destruction.

What these artists and others such as Francesca Woodman, Chris Killip, Paul Graham and Hannah Collins do is show that although photography and video are common mediums available to us all, they are developing ones, too, and their expressive possibilities are infinite.