Cite as: 598 U. S. ____ (2023) 5 Syllabus presented as agnostic as to the nature of the content. At bottom, the allegations here rest less on affirmative misconduct and more on passive nonfeasance. To impose aiding-and-abetting liability for passive nonfeasance, plaintiffs must make a strong showing of assistance and scienter. Plaintiffs fail to do so. First, the relationship between defendants and the Reina attack is highly attenuated. Plaintiffs make no allegations that defendants’ relationship with ISIS was significantly different from their arm’s length, passive, and largely indifferent relationship with most users. And their relationship with the Reina attack is even further removed, given the lack of allegations connecting the Reina attack with ISIS’ use of these platforms. Second, plaintiffs provide no reason to think that defendants were consciously trying to help or otherwise participate in the Reina attack, and they point to no actions that would normally support an aiding-and-abetting claim. Plaintiffs’ complaint rests heavily on defendants’ failure to act; yet plaintiffs identify no duty that would require defendants or other communication-providing services to terminate customers after discovering that the customers were using the service for illicit ends. Even if such a duty existed in this case, it would not transform defendants’ distant inaction into knowing and substantial assistance that could establish aiding and abetting the Reina attack. And the expansive scope of plaintiffs’ claims would necessarily hold defendants liable as having aided and abetted each and every ISIS terrorist act committed anywhere in the world. The allegations plaintiffs make here are not the type of pervasive, systemic, and culpable assistance to a series of terrorist activities that could be described as aiding and abetting each terrorist act by ISIS. In this case, the failure to allege that the platforms here do more than transmit information by billions of people—most of whom use the platforms for interactions that once took place via mail, on the phone, or in public areas—is insufficient to state a claim that defendants knowingly gave substantial assistance and thereby aided and abetted ISIS’ acts. A contrary conclusion would effectively hold any sort of communications provider liable for any sort of wrongdoing merely for knowing that the wrongdoers were using its services and failing to stop them. That would run roughshod over the typical limits on tort liability and unmoor aiding and abetting from culpability. Pp. 21–27. (2) The Ninth Circuit’s analysis obscured the essence of aidingand-abetting liability. First, the Ninth Circuit framed the issue of substantial assistance as turning on defendants’ assistance to ISIS’ activities in general, rather than with respect to the Reina attack. Next, the Ninth Circuit misapplied the “knowing” half of “knowing and substantial assistance,” which is designed to capture the defendants’ state