Pon farr was the Vulcan time of mating and was thus a major part of the reproductive cycle. The pon farr occurred approximately once every seven years during adulthood. During pon farr, a Vulcan lost all emotional control and had to address the condition or risk death. Mating was the most usual way to successfully resolve pon farr, but ritual combat and intensive meditation were also used. (TOS episode & novelization: Amok Time; TOS movie, novelization & comic adaptation: The Search for Spock, VOY episode: "Blood Fever")
During the onset of the pon farr, the Vulcan underwent a neurochemical imbalance. Early symptoms included restlessness, lack of emotional control, and thoughts of the opposite sex. As it progressed, the Vulcan found it harder to suppress emotional and aggressive outbursts and felt great sexual desire for a bonded mate. He felt protective and possessive of his mate and was willing to fight anyone who might threaten his mating rights. Vulcans referred to these urges as "the Fires." His condition sometimes triggered the blood fever in his bonded mate. (TOS novel: Vulcan's Heart) The last stage was plak tow. Unless the pon farr was satisfied, the Vulcan would die within eight days of the process beginning. (TOS episode: "Amok Time"; VOY episode: "Blood Fever")
On Voyager, a hologram of a Vulcan female successfully met Vorik's sexual needs. Vorik had been betrothed to a Vulcan woman but was not married. He believed his betrothed would have found another mate during his long absence. Later, Tuvok mated with a hologram of his wife to resolve his pon farr. (VOY episodes: "Blood Fever", "Body and Soul")
Vulcan women might enter pon farr and also risked death if they failed to mate when their bonded mates experienced the condition. (TOS novels: Dwellers in the Crucible, Mind Meld, Vulcan's Heart, The Pandora Principle)
In the days before Vulcans embraced Surak's teachings of peace and logic, Vulcans undergoing the pon farr would often kill in order to win a mate. After the Time of Awakening however, the koon-ut-kal-if-fee was adopted, and Vulcans became telepathically bonded when they were young (TOS episode: "Amok Time") during the betrothal ceremony, or koon-ut-la. (TOS novel: Mind Meld The telepathic link led the couple to one another when the male entered pon farr.
Due to the very private nature of the pon farr within Vulcan society, outsiders were not told of it, and Starfleet doctors only began to find out in the 23rd century. Even by the 2370s, medical knowledge about the pon farr was scarce. (VOY episode: "Blood Fever")
Despite being a Vulcan offshoot, the Romulans did not go through pon farr, having removed it from their genome with genetic engineering after the Sundering. (TOS - Rihannsu novel: The Romulan Way) However, this was not true in all instances. A Romulan boy who was bonded with Spock's young Vulcan female relative did go through pon farr, demonstrating that Romulans and Vulcans were descended from the same stock. (TOS novel: Mind Meld)