Lifestreaming is an act of documenting and sharing aspects of one's daily experiences online, via a lifestream website that publishes things of a person's choosing (e.g. photos, social media, videos).

The term "lifestream" was coined by Eric Freeman and David Gelernter at Yale University in the mid-1990s to describe "...a time-ordered stream of documents that functions as a diary of your electronic life; every document you create and every document other people send you is stored in your lifestream. The tail of your stream contains documents from the past (starting with your electronic birth certificate). Moving away from the tail and toward the present, your stream contains more recent documents—papers in progress or new electronic mail; other documents (pictures, correspondence, bills, movies, voice mail, software) are stored in between. Moving beyond the present and into the future, the stream contains documents you will need: reminders, calendar items, to-do lists. The point of lifestreams isn't to shift from one software structure to another but to shift the whole premise of computerized information: to stop building glorified file cabinets and start building (simplified, abstract) artificial minds; and to store our electronic lives inside."

The concept existed long before it was first introduced to the public. Globally known public figures like Leonardo da Vinci and Albert Einstein were collecting their stream of personal and professional data, an act that could be considered lifestreaming.

I like to think of a lifestreaming as today's digital equivalent of Leonardo da Vinci's notebooks [...] da Vinci's recorded notes, drawing, questions and more in his notebooks. Some of these were quite mundane (grocery lists and doodles), others were not. But their body of work was overtime, a view of a one individual's mind.

— Steve Rubel, Why Lifestream? To model Leonardo da Vinci diaries.

Social network aggregators adapted Freeman and Gelernter's original concept to address the vast flows of personal information and exchange created by social network services such as MySpace or Facebook ("web companies large and small are embracing this stream" of providing lifestreaming). Other online applications have emerged to facilitate a user's lifestream. Posterous offered a variety of unique features to enhance its basic blogging function. Tumblr is a similar concept, but with slightly different features.

Websites accommodating of lifestreaming gather together all the information someone wants to display and order it in reverse-chronology. "Each person designs her daily life to some extent-for instance basic time management tools. Putting one's life online might provide the critical perspective to help redesign it. It is not just an organizational tool, but a tool that allows critical evaluation, reassessment and tweaking daily choice"

However, there is a clear distinction between the act of lifestreaming as a simple form of editorial extension to one's activity stream, and the production of a well-designed lifestream which involves commitment and requires the technical skills necessary to create and maintaining its underlying site.