High-frequency trading, as distinct from other forms of algorithmic trading, is of little or no social value. Implementation of resting rules would retain the benefits of algorithmic trading while eliminating the potential harm of high-frequency trading.

I investigate the competition between suppliers of components of a system for which there are network effects among users. Bundling one of these components with an outside good reduces the cost to consumers of using the system. This cost reduction is not necessarily welfare-enhancing, and...