Absent-mindedness is a mental state wherein a person is forgetfully inattentive. It is the opposite mental state of mindfulness.

Absent-mindedness is often caused by things such as boredom, sleepiness, rumination, distraction, or preoccupation with one's own internal monologue. When experiencing absent-mindedness, people exhibit signs of memory lapses and weak recollection of recent events.

Absent-mindedness can usually be a result of a variety of other conditions often diagnosed by clinicians such as attention deficit hyperactivity disorder (ADHD) and depression. In addition to absent-mindedness leading to an array of consequences affecting daily life, it can have more severe, long-term problems.

Absent-mindedness seemingly consists of lapses of concentration or "zoning out". This can result in lapses of short or long-term memory, depending on when the person in question was in a state of absent-mindedness. Absent-mindedness also relates directly to lapses in attention. Schachter and Dodsen of the Harvard Psychology department say that in the context of memory, "absent-mindedness entails inattentive or shallow processing that contributes to weak memories of ongoing events or forgetting to do things in the future".

Though absent-mindedness is a frequent occurrence, there has been little progress made on what the direct causes of absent-mindedness are. However, it tends to co-occur with ill health, preoccupation, and distraction.

The condition has three potential causes:

Absent-mindedness is also noticed as a common characteristic of personalities with schizoid personality disorder.

Lapses of attention are clearly a part of everyone's life. Some are merely inconvenient, such as missing a familiar turn-off on the highway, while some are extremely serious, such as failures of attention that cause accidents, injury, or loss of life. Sometimes, lapses of attention can lead to a significant impact on personal behaviour, which can influence an individual's pursuit of goals. Beyond the obvious costs of accidents arising from lapses in attention, there are lost time; efficiency; personal productivity; and quality of life. These can also occur in the lapse and recapture of awareness and attention to everyday tasks. Individuals for whom intervals between lapses are very short are typically viewed as impaired. Despite the prevalence of attentional failures in everyday life, relatively little work has been done to directly measure individual differences in everyday errors arising from propensities for failures of attention. Absent-mindedness can also lead to bad grades at school, boredom, and depression.