Telepathy was the very basic ability to read minds, mentally communicate and project the user's thoughts over small or vast distances with other individuals.
Every Force user, Jedi or Sith, was potentially able to use this ability. The range of telepathy itself is theoretically infinite, but the telepath must be able to sense the presences of those they wish to contact. Thus, communicating with non-Force-sensitives became nearly impossible over distances greater than a handful of kilometers, and the typical upper limit for Force-sensitives was approximately 1,000 kilometers. However, individuals who either shared a biological relationship or a particularly strong emotional bond were known to communicate across far greater ranges. In extreme cases (such as the twin bond between Jacen and Jaina Solo), the link apparently had no spacial limit.
The telepathy of most Force-sensitive individuals were not potent enough to truly read the thoughts of other beings, and could only sense the emotions or general mindset of those around them. This form of basic telepathy was more commonly known as Force empathy. While every Force-adept was able to use telepathy to some degree, very few of them were actually skilled enough to participate in actual telepathic conversations. Most Force-sensitive individuals could only exchange short four or five-word sentences to those that they shared close bonds with. Usually, Jedi employed telepathy only to read the states of minds or engage in silent communication. Eye contact, in part, allowed a user to have less difficulty in focusing on a target's thoughts. A very skilled user could create a telepathic shield to isolate their own brain waves, intercept stray thoughts, screen multiple minds simultaneously, whisper across space, yell without noise, keep secrets, and uncover the truths under layers of deceits and hidden memories. Adept pilots could even be able to seek information from other stars so as to navigate a starship through hyperspace without use of a nav computer. Moreover, telepathy also gave its user an advantage in combat, as it could be used to predict the next movement of an opponent, and furthermore to taunt and confuse opponents by echoing their voice in their head in every direction, masking the users position. Another telepathic abilities was to induce pain or project a telepathic blast to hurt the target's mind, as well as extract information for a person's mind causing them extreme pain, also known as Mind Probe.
Some species, such as the Iktotchi, the Anzati, the Hortek, the Quermians, Zeltrons, Umbarans, and the Draethos, had evolved a natural telepathic ability, common even to those of their number who could not touch the Force. When trained as Jedi, their natural talents were often magnified a thousandfold or more. This was the case with Saesee Tiin, whose natural prowess in the ability caused him great discomfort during his years as a Padawan. It was not until he was trained by Jedi Master Omo Bouri that he learned to better control his telepathic sense. Some Lamproids exhibited natural telepathy, although this was not a species-wide trait.
As telepathy was a very basic use of the Force, the relatively untrained Luke Skywalker was able to employ it to reach out to his twin sister Leia Organa and call for her help during the Occupation of Bespin. Vader then (as Luke and the group were escaping) called out to Luke to again convince him to join him and embrace the dark side. The fact that the three were related allowed them to reach out over even greater distances.
Drain Knowledge was a technique that utilized telepathy in a violent manner, as it forcibly extracted information from the victim while potentially causing psychological damage. Similarly, Memory Walk was a technique that allowed a user to reach into the victim's mind, force them to repeatedly relive their most uncomfortable memories, and could potentially even cause physical pain.
Neural Storm was a telepathic ability that used psychic energy to overload a victim's neural network, causing extreme but momentary disorientation.