Stalking is any willful and repeated action that would cause a reasonable person to feel harassed, frightened, or intimidated. While many people believe that stalkers are harmless, and best if left alone, stalking is a very serious crime that can, and often does, escalate to physical violence and/or sexual assault.
Stalking can take many forms. Here is a list of common means of contact used by stalkers:
The majority of stalkers use multiple of means of contact.
You'll notice that often one single incidence of these alone would not raise alarm with most people. But when they are repeated and the effect is that the target is made afraid or intimidated, they take on a much more sinister appearance and constitute a violation of a person's privacy and sense of well-being, as well as breaking the law.
(Courtesy Steve Thompson, Central Michigan University Sexual Aggression Services Coordinator)