The person keeps trying to arrange contact or have conversations with you, even though you feel there is no longer any point.

By itself, this is rarely considered stalking; most people view this as a person simply trying to get a date or patch up a relationship. At stage 1, the victim rarely realizes that this is going to become an escalating problem.

The person keeps trying to arrange contact or have conversations with you or gather information about you -- even though the events are now making you feel profoundly uncomfortable. The person's persistence seems a bit "crazy" and although they are not physically demonstrative, their behavior seems somehow "scary" to you anyway. This may be the stage where you realize this person has become a stalker.

During contact they don't seem self-conscious; they don't seem to realize that they're behaving bizarrely. If others witness these events, the behavior seems irrational to them. (Some clueless persons will think you're the one being irrational, for being disturbed by the stalker. Don't let outsiders tell you how to feel or not feel!)

Interference is any contact or activity that they engage in with others, which disturbs your right to live your life without interference.  It includes their distributing private information about you to other people, contacting other people to try to have discussions about you, etc.

This is the stage at which it becomes obvious that it's a stalking situation, even if you or your friends had been trying to believe that it wasn't.

Contact attempts now include veiled threats and/or physical aggression. A veiled threat is something like "you'll be sorry" -- it is not the same thing as an outright threat such as "I'm going to hit you." Physical aggression includes trying to stand in your way, blocking your path, walking toward you while yelling -- it is not the same thing as physical contact (violence).

Illegal interference includes slander, libel, blackmail, distributing photos of you when they don't have a legal model release, etc.

Make sure you have thorough documentation of any stage 1 or stage 2 behavior, and when you get a stage 3 occurrence, call the police to file a report.

Clearly stated threats of what they would like to do, or what they intend to do.

Vandalism or destruction of your belongings, your environment, etc.

Violence toward yourself, those around you, your pets, or animals in your environment.  Abduction, assault, etc.