Plaintiffs alleging parallel conduct among competitors as a Sherman Act section 1 conspiracy must allege additional facts (plus factors) that place that parallel conduct in a context suggesting a preceding agreement. Here, only one of the eight plus factors plaintiffs alleged weighed slightly in favor of conspiracy, which was insufficient to cross the threshold from possible to plausible. The three DRAM manufacturers decreased the amount by which they increased production of DRAMs in response to an oversupply in the market and declining prices. Samsung went first. Its two lesser competitors followed a month later. This suggested consciously parallel action and following Samsung’s market leadership, but not a prior agreement to do so. Cutting production helped all three manufacturers individually to raise prices and profitability, so there was independent reason to take that action.