Incumbent ecosystem operators can abuse their ecosystem power to foreclose competition and harm consumers. Ecosystem harms exhibit themselves in long-term harms to competition that are hard to capture. Abuses of dominance or gatekeeper power are relatively visible, but ecosystem harms require long-term strategies that span across markets to harm competition by means of non-structural power. The chapter explains how ecosystem harms can be understood and gives four examples of clear harms associated with ecosystem power; entrenchment harms, industry wide foreclosure due to industry roll-ups, the softening of competition, and harms to innovation.