Can simple biological systems be built from standard, interchangeable parts and operated in living cells? Or is biology simply too complicated to be engineered in this way? The international Genetically Engineered Machine Competition (iGEM) is an open design challenge for student teams that addresses this difficult question. Using a library of standardised parts known as BioBricks, groups of undergraduates from around the world spend their summer designing and assembling biological devices, to build genetic machines.