Intrapersonal communication is communication with oneself or self-to-self communication. Examples are thinking to oneself "I'll do better next time" after having made a mistake or having an imaginary conversation with one's boss because one intends to leave work early. It is often understood as an exchange of messages in which the sender and the receiver is the same person. Some theorists use a wider definition that goes beyond message-based accounts and focuses on the role of meaning and making sense of things. Intrapersonal communication can happen alone or in social situations. It may be prompted internally or occur as a response to changes in the environment. The term "autocommunication" is sometimes used as a synonym.

Intrapersonal communication encompasses a great variety of phenomena. A central type happens purely internally as an exchange within one's mind. Some researchers see this as the only form. In a wider sense, however, there are also types of self-to-self communication that are mediated through external means, like when writing a diary or a shopping list for oneself. For verbal intrapersonal communication, messages are formulated using a language, in contrast to non-verbal forms sometimes used in imagination and memory. One distinction among inner verbal forms is between self-talk and inner dialogue. Self-talk involves only one voice talking to itself. For inner dialogue, several voices associated with different positions take turns in a form of imaginary interaction. Other phenomena associated with intrapersonal communication include planning, problem-solving, perception, reasoning, self-persuasion, introspection, and dreaming.

Models of intrapersonal communication discuss which components are involved and how they interact. Many models hold that the process starts with the perception and interpretation of internal and external stimuli or cues. Later steps involve the symbolic encoding of a message that becomes a new stimulus. Some models identify the same self as sender and receiver. Others see the self as a complex entity and understand the process as an exchange between different parts of the self or between different selves belonging to the same person. Intrapersonal communication contrasts with interpersonal communication, in which the sender and the receiver are distinct individuals. The two phenomena influence each other in various ways. For example, positive and negative feedback received from other people affects how a person talks to themself. Intrapersonal communication is involved in interpreting messages received from others and in formulating responses. Because of this role, some theorists hold that intrapersonal communication is the foundation of all communication. But this position is not generally accepted and an alternative is to hold that intrapersonal communication is an internalized version of interpersonal communication.

Because of its many functions and influences, intrapersonal communication is usually understood as a significant psychological phenomenon. It plays a key role in mental health, specifically in relation to positive and negative self-talk. Negative self-talk focuses on bad aspects of the self, at times in an excessively critical manner. It is associated with psychological stress, anxiety, and depression. Steps commonly associated with countering negative self-talk are to become aware of negative patterns, to challenge the truth of overly critical judgments, and to foster more positive patterns of thought. Of special relevance in this regard is the self-concept, i.e. how a person sees themself, specifically their self-esteem or how they evaluate their abilities and characteristics. Intrapersonal communication is not as thoroughly researched as other forms of communication. One reason is that it is more difficult to study since it happens primarily as an internal process. Another reason is that the term is often used in a very wide sense making it difficult to demarcate which phenomena belong to it.