The evidence. Alongside the biblical books, most of the scrolls are the community's own literature, rulebooks, hymns, and Bible commentaries that describe a devout, strict, priestly Jewish group living apart in the desert. They include the Community Rule (its initiation, shared property, and discipline), the War Scroll (a coming battle of "the sons of light against the sons of darkness"), the Thanksgiving Hymns, the Temple Scroll, and the pesharim, running verse-by-verse commentaries that read the prophets as fulfilled in the group's own day and leader, the "Teacher of Righteousness."
The leading explanation (an argument, widely held). Roland de Vaux and many after him identified this group with the Essenes, a Jewish sect described by three ancient writers, the historian Josephus, the philosopher Philo, and the Roman Pliny the Elder, who even locates an Essene settlement on the western shore of the Dead Sea, right where Qumran sits. On this reading the Essenes lived at Qumran, copied and wrote the scrolls, and hid them in the caves as the Romans advanced in AD 68. It is the majority view and fits a great deal of the evidence.
The counter-cases (attributed, no winner). But it is a reconstruction, not a signed record, and serious scholars have pushed back: some (notably Norman Golb) argue the scrolls were not written at Qumran at all but are a broader library evacuated from Jerusalem and hidden in the desert for safekeeping; others question whether Qumran was even a religious settlement rather than, say, a villa or a fort. The scrolls themselves never use the word "Essene." So the honest formula is: a distinctive Jewish community's writings are a fact; that the community was the Essenes living at Qumran is the best-supported argument, held by most but not all, and this file gives both the majority identification and the dissent. Their vocabulary of "sons of light" (John 12:36) and their retreat to the wilderness of Judea, where John the Baptist would also preach (Matthew 3:1), open the window this file's next paragraph looks through.