At its core, Section 2 of the Sherman Act makes it illegal to acquire or maintain monopoly power through improper means. The long-standing requirement for monopolization is both "(1) the possession of monopoly power in the relevant market and (2) the willful acquisition or maintenance of that power as distinguished from growth or development as a consequence of a superior product, business acumen, or historic accident."
Regarding the first element of Section 2, it is "settled law" that the offense of monopolization requires "the possession of monopoly power in the relevant market." Monopoly power means substantial market power that is durable rather than fleeting — market power being the ability to raise prices profitability above those that would be charged in a competitive market.
But, as the second element of Section 2 makes clear, "the possession of monopoly power will not be found unlawful unless it is accompanied by an element of anticompetitive conduct." Such conduct often is described as “exclusionary” or "predatory” conduct. This element includes both conduct used to acquire a monopoly unlawfully and conduct used to maintain a monopoly unlawfully. A wide range of unilateral conduct has been challenged under Section 2, and it often can be difficult to determine whether the conduct of a firm with monopoly power is anticompetitive.