If there is any consensus in the debate over how to revitalize the American economy, it is over innovation. Innovation, we can all readily concur, is the only way for an advanced economy like the United States – which cannot grow by copying and imitating others – to continue to boost productivity and raise living standards. But understanding why useful innovations occur, and what if anything governments can do to foster them, quickly degenerates into a clash between free market absolutists and industrial policy aficionados.