Stalking is unwanted or obsessive attention by an individual or group towards another person. Stalking behaviors are related to harassment and intimidation and may include following the victim in person or monitoring them. The term stalking is used with some differing definitions in psychiatry and psychology, as well as in some legal jurisdictions as a term for a criminal offense.
According to a 2002 report by the U.S. National Center for Victims of Crime, "virtually any unwanted contact between two people that directly or indirectly communicates a threat or places the victim in fear can be considered stalking", although in practice the legal standard is usually somewhat more strict.
People characterized as stalkers may be accused of having a mistaken belief that another person loves them (erotomania), or that they need rescuing. Stalking can sometimes consist of an accumulation of a series of actions which in themselves can be legal, such as calling on the phone, sending gifts, or sending emails.
In the UK, for example, most stalkers are former partners and evidence indicates that the mentally ill stalking type of behaviour propagated in the media occurs in only a minority of cases of alleged stalking.
Psychological effects on victims
Disruptions in daily life necessary to escape the stalker, including changes in employment, residence and phone numbers, may take a toll on the victim's well-being and lead to a sense of isolation.
According to Lamber Royakkers:
"Stalking is a form of mental assault, in which the perpetrator repeatedly, unwantedly, and disruptively breaks into the life-world of the victim, with whom they have no relationship (or no longer have). Moreover, the separated acts that make up the intrusion cannot by themselves cause the mental abuse, but do taken together (cumulative effect)."
Types of victims
Based on their work with stalking victims for eight years in Australia, Mullen and Pathé identified different types of stalking victims dependent on their previous relationship to the stalker. These are:
1. Prior intimates: Victims who had been in a previous intimate relationship with their stalker. In the article, Mullen and Pathé describe this as being "the largest category, the most common victim profile being a woman who has previously shared an intimate relationship with her (usually) male stalker." These victims are more likely to be exposed to violence being enacted by their stalker especially if the stalker had a criminal past. In addition, victims who have "date stalkers" are less likely to experience violence by their stalkers. A "date stalker" is considered an individual who had an intimate relationship with the victim but it was short-lived.
2. Casual acquaintances and friend: Amongst male stalking victims, most are part of this category. This category of victims also includes neighbor stalking. This may result in the victims' change of residence.
3. Strangers: These victims are typically unaware of how their stalkers began stalking because typically these stalkers form a sense of admiration for their victims from a distance.
4. The famous: Most of these victims are individuals who are portrayed heavily on media outlets but can also include individuals such as politicians and athletes.

Types of stalkers
Psychologists often group individuals who stalk into two categories: psychotic and nonpsychotic. Stalkers may have pre-existing psychotic disorders such as delusional disorder, schizoaffective disorder, or schizophrenia. Most stalkers are nonpsychotic and may exhibit disorders or neuroses such as major depression, adjustment disorder, or substance dependence, as well as a variety of Axis II personality disorders (such as antisocial, borderline, dependent, narcissistic, or paranoid).
Some of the symptoms of "obsessing" over a person may be characteristic of obsessive compulsive personality disorder. The nonpsychotic stalkers' pursuit of victims can be influenced by various psychological factors, including anger, hostility, projection of blame, obsession, dependency, minimization, denial, and jealousy. Conversely, as is more commonly the case, the stalker has no antipathic feelings towards the victim, but simply a longing that cannot be fulfilled due to deficiencies either in their personality or their society's norms.

In "A Study of Stalkers" Mullen et al.. (2000) identified five types of stalkers:
1. Rejected stalkers follow their victims in order to reverse, correct, or avenge a rejection (e.g. divorce, separation, termination).
2. Resentful stalkers make a vendetta because of a sense of grievance against the victims – motivated mainly by the desire to frighten and distress the victim.
3. Intimacy seekers seek to establish an intimate, loving relationship with their victim. Such stalkers often believe that the victim is a long-sought-after soul mate, and they were 'meant' to be together.
4. Incompetent suitors, despite poor social or courting skills, have a fixation, or in some cases, a sense of entitlement to an intimate relationship with those who have attracted their amorous interest. Their victims are most often already in a dating relationship with someone else.
5. Predatory stalkers spy on the victim in order to prepare and plan an attack – often sexual – on the victim.
Many stalkers fit categories with paranoia disorders. Intimacy-seeking stalkers often have delusional disorders involving erotomanic delusions. With rejected stalkers, the continual clinging to a relationship of an inadequate or dependent person couples with the entitlement of the narcissistic personality, and the persistent jealousy of the paranoid personality. In contrast, resentful stalkers demonstrate an almost "pure culture of persecution", with delusional disorders of the paranoid type, paranoid personalities, and paranoid schizophrenia.

And women were more likely (much more likely) to be violent if they were stalking a victim with whom they had a prior history of sexual intimacy.

Credit: Wikipedia.org