“Information operations” or “psychological operations” have long been part of armed conflicts. Among Western militaries, they are commonly understood as the employment of communication or other means to influence the views, attitudes, or behavior of adversaries or civilian populations to achieve political and military objectives. Chinese military strategy describes “psychological offense and defense” as “a combat action that uses specific information and media to influence the psychology and behavior of the target object through rational propaganda, deterrence and emotional guidance based on strategic intentions and combat missions.” Likewise, Russian military doctrine elaborates on concepts such as “psychological warfare” and on “war against mentality.” Non-State armed groups conduct such operations, too. With the rapid growth of information and communication technology over the past decade, the scale, speed, and reach of information or psychological operations have increased significantly, raising concerns about their possible humanitarian impact. While international humanitarian law permits information and psychological operations that are militarily necessary as part of military operations, it imposes limits, in particular, on those that are directed against either civilians or military personnel hors de combat and can be reasonably expected to cause harm. This article analyzes these and other limits that international humanitarian law sets on information or psychological operations during armed conflicts.