The problem of conflicts of interest began to receive serious attention in the medical literature in the 1980s. A conflict of interest is a set of conditions in which professional judgment concerning a primary interest tends to be unduly influenced by a secondary interest. Conflict-of-interest rules, informal and formal, regulate the disclosure and avoidance of these conditions. The primary interest is determined by the professional duties of a physician, scholar, or teacher. The secondary interest is usually not illegitimate in itself, and indeed it may even be a necessary and desirable part of professional practice. Conflict-of-interest rules usually focus on financial gain, not because it is more pernicious than other secondary interests but because it is more objective and more fungible. A common criticism of rules governing conflicts of interest is that they unfairly punish ethical physicians and researchers for the misdeeds of the few unethical ones.