The Quantified Self is a movement to incorporate technology into data acquisition on aspects of a person's daily life in terms of inputs (e.g. food consumed, quality of surrounding air), states (e.g. mood, arousal, blood oxygen levels), and performance (mental and physical). Such self-monitoring and self-sensing, which combines wearable sensors (EEG, ECG, video, etc.) and wearable computing, is also known as lifelogging or sousveillance. Other names for using self-tracking data to improve daily functioning are “self-tracking”, "auto-analytics", “body hacking” and “self-quantifying”.

The movement was started under the name "Quantified Self" by Wired Magazine editors Gary Wolf and Kevin Kelly in 2007 as "a collaboration of users and tool makers who share an interest in self knowledge through self-tracking". In 2010, Wolf spoke about the movement at TED, and in May 2011 the first international conference was held in Mountain View, California.