While P2P systems had previously been used in many application domains,
 the concept was popularized by
file sharing systems such as the music-sharing application
Napster (originally released in 1999). The peer-to-peer movement allowed millions of Internet users to connect "directly, forming groups and collaborating to become user-created search engines, virtual supercomputers, and filesystems."
 The basic concept of peer-to-peer computing was envisioned in earlier software systems and networking discussions, reaching back to principles stated in the first
Tim Berners-Lee's vision for the
World Wide Web was close to a P2P network in that it assumed each user of the web would be an active editor and contributor, creating and linking content to form an interlinked "web" of links. The early Internet was more open than present day, where two machines connected to the Internet could send packets to each other without firewalls and other security measures.
 This contrasts to the
broadcasting-like structure of the web as it has developed over the years.
 As a precursor to the Internet,
ARPANET was a successful client-server network where "every participating node could request and serve content." However,
ARPANET was not self-organized, and it lacked the ability to "provide any means for context or content-based routing beyond 'simple' address-based routing."
Therefore, a distributed messaging system that is often likened as an early peer-to-peer architecture was established:
USENET was developed in 1979 and is a system that enforces a
decentralized model of control. The basic model is a client-server model from the user or client perspective that offers a self-organizing approach to newsgroup servers. However,
news servers communicate with one another as peers to propagate
Usenet news articles over the entire group of network servers. The same consideration applies to
SMTP email in the sense that the core email-relaying network of
mail transfer agents has a peer-to-peer character, while the periphery of
e-mail clients and their direct connections is strictly a client-server relationship.
In May 1999, with millions more people on the Internet,
Shawn Fanning introduced the music and file-sharing application called Napster.
 Napster was the beginning of peer-to-peer networks, as we know them today, where "participating users establish a virtual network, entirely independent from the physical network, without having to obey any administrative authorities or restrictions."