Telepathy is a basic psionic power, possessed by various species.
- Main article: Protoss mental abilities
The protoss possess telepathy universally. Indeed, they are so proficient at it that during the Aeon of Strife, protoss could even prevent others from gaining access to their minds without technological devices. Protoss are able to read the minds of terrans with ease, but possess enough self control to not read such thoughtstreams.
The Khala-following protoss of present times cannot completely hide their thoughts from each other, but the ability can still be used to a degree. The amount of privacy in a conversation is up to the protoss involved in it and their level of psionic control, able to fine-tune their thoughts to such an extent that "mental spikes" may be generated, causing pain to their recipients.
Protoss telepathy is compatible with their technology, such as psychic boosters and psychic communication loops, allowing the dispatch and receiving of psychic messages on a large scale and from great distances.
Terrans have the potential to become a potent psionic race in only a few generations, although psychic abilities are currently rare. Terran psychic power is measured on the Psionic Index; most terrans have a PI of 2 or less. The inner thoughts of terrans rarely correspond to how they present themselves to those around them.
A few terran individuals possess telepathy. Most of these individuals become ghosts, who generally have a PI of 5 or 6. However, the degree of telepathy varies; the ability to sense surface thoughts is seemingly universal for such individuals although to directly read an individual's thoughts is not as common. Reading thoughts unintentionally is generally a given for telepaths and some are never able to completely filter external thoughts. This can create "feedback loops", where a person's thoughts is mirrored by the telepath. External fear becomes the telepath's fear, external anger becomes the telepath's anger, etc. These thoughts are even capable of manifesting in the dreams of a telepath and dreams, or the lack of them, can be read directly. However, with enough training, it is not impossible for a terran to prevent him/herself from doing so. In addition, non-telepaths, with enough willpower, can keep their thoughts to themselves. Some telepaths can resist mind-reading attempts and/or generate false surface thoughts in order to avoid suspicion. Dominion regulations prohibit telepaths in their service from reading officials' minds without just cause—an individual's rank plays a role in this.
Psychics with a PI value of less than 5 have difficulty creating telepathic messages or creating "mental maps".
Terran minds go blank as the body of the respective individual goes into shock and/or nears death.
The zerg are entirely telepathic, but in a different manner to the protoss. While each protoss individual is his/her own self, the zerg utilized a mental hierarchy, with the Overmind at the top, moving down to cerebrates, overlords, queens, and steadily down to lesser strains. These strains are capable of 'speech', but are incapable of ignoring the directives of higher strains. Although the Queen of Blades has taken the role of the Overmind at the top of the zerg hierarchy, the process remains the same.
To date, no thoughts of lesser strains have ever been known to be read by a protoss or terran telepath. The only known exception is Jim Raynor, who was able to hear the zerg 'speaking' whilst on Char. This was due to Kerrigan weilding her telepathy clumsily, and filtering her unwanted thoughts into Raynor whilst she came to accept who and what she had become. The protoss Zeratul was aware of this, but could not hear the zerg's thoughts. During a mission to Altara, Nova was able to sense a mass of zerg thought that corresponded to approaching zerg, but couldn't sense the individual elements of the thought mass.
Higher strains are a different story however, as Zeratul was able to communicate with the cerebrate Zasz via telepathy before assassinating the creature. Upon doing so, his mind connected with that of the Overmind, their thoughts being exchanged. The Overmind learnt of the location of the protoss homeworld of Aiur, while Zeratul learnt of the zerg's origins and goal of assimilating the protoss race. The emotions of higher strains can be mirrored by lower strains, akin to a feedback loop.