The global future of nuclear power may rest in large part on local politics, reports Geoff Brumfiel. On 28 April 1986 the Soviet Union acknowledged that there had been an accident in the Chernobyl nuclear power plant in Ukraine two days earlier. This week's cover shows a helicopter crew monitoring radioactivity above the damaged reactor 4 later that summer. In a series of pieces in this issue we chart the costs of Chernobyl, the world's worst peacetime nuclear accident, in terms of human lives and ecological damage. And with the perspective of 20 years, it's time also to assess the prospects for nuclear energy in the twenty-first century. In a Commentary anticipating the UN agencies' forthcoming Chernobyl report, Dillwyn Williams and Keith Baverstock stress the importance of comprehensive health monitoring of populations in the most affected areas of Belarus, Ukraine and Russia. Without it, the nuclear power industry will never overcome the public suspicion that is a lasting legacy of Chernobyl.