They need not necessarily be mediated by a physical grid. The adoption of particular software, the “buzz” created by viral marketing around a particular product, the positive spillovers of a company’s research and development (R&D) spending or a “clusteri of like-minded researchers pushing each other are all examples where positive externalities ensure that the final result is greater than the sum of the individual contributions. Whether negative or positive, technical externalities lead to suboptimal situations as their unconstrained production is either too high or too low.