Potential Slayers were girls born with the potential to become the Slayer, chosen by mystical forces.
Originally, only one Slayer would be called at a time, activated after the previous one had died. However, there were many "Potentials" all over the world, any one of which could be chosen.
Potentials lacked the true power of the Slayer, but had greater strength, coordination, agility, and speed than normal human teenagers. Potentials also experienced strange dreams of being Slayers from the past as well as having premonitions of the supernatural.
In most cases, these girls were identified by the Watchers Council and assigned a Watcher to guide and train them so that they would be prepared if they were called to be the Slayer. For example, Kendra Young was given to her Watcher when she was an infant.
Since the Watchers themselves had only a vague understanding of the forces that selected the Slayer however, they were unable to identify every Potential in the world. There were many cases where the girl was completely oblivious to her calling, and remained that way unless she was activated as the new "chosen one." Buffy Summers was one such Potential, only becoming aware of her status when her predecessor was killed and her first Watcher, Merrick, found her.
Buffy's death and resurrection in late 2001 disrupted the mysterious mystical forces surrounding the Slayer, so in 2002, the First Evil used this as a catalyst to destroy the Slayer line. It dispatched an army of Bringers to kill as many potentials as possible, including their watchers, eventually planning to murder Slayer Faith Lehane and then finally Buffy. Rupert Giles, one of the only Watchers left, began bringing as many potentials as he could track down to Buffy's home in Sunnydale. Those who didn't die, Buffy trained to become an army for her final battle with The First, the Bringers, and the Turok-Han.Buffy asked Willow Rosenberg to tap into the essence of the slayer Scythe to activate every Potential around the world. 
Almost a year and a half after the spell was cast, nearly 1800 new Slayers were active around the world, though only a certain amount of them were working with the Slayer Organization. The girls were called when they reached a "coming of age".
After Buffy destroyed the Seed of Wonder, cutting off magic from this dimension, no more Slayers could be called. However, girls were still born with the potential to be Slayers if magic ever returned, which occurred in the 23rd Century, allowing Melaka Fray to be activated as the first Slayer in nearly 200 years.
List of Potential Slayers
- Amanda (activated; killed)
- Annabelle (not activated; killed)
- "Buffy Summers" [Underground decoy] (activated; killed)
- Caridad (activated)
- Chao-ahn (activated)
- Chloe (not activated; killed herself)
- Colleen (presumably activated)
- Dianne (not activated; killed)
- Dominique (presumably activated)
- Eve (not activated; killed)
- German Potential Slayer (not activated; killed)
- Injured Girl (activated)
- Istanbul Potential Slayer (not activated; killed)
- Kennedy (activated)
- Molly (not activated; killed)
- Nora (not activated; killed)
- Rona (activated)
- Shannon (activated)
- Soledad (activated; killed)
- Violet (activated)