Elements of Stalking
The crime of Stalking is committed when a person willfully, maliciously, and “repeatedly follows” or willfully and maliciously “harasses” another person and makes a “credible threat” intending to frighten that person and if the person believes they or an immediate family member is in danger of serious injury.
A specific exception is conduct that occurs during labor picketing.
To commit the offense the victim must at the time of the incident(s) underlying the charges be intimidated or frightened by of defendant’s behavior. 
The constitutionality of the crime has repeatedly been challenged unsuccessfully in the courts.
There are several offenses in the Penal Code related to Stalking including criminal threats under section 422; trespass to carry out threat under section 601; telephone harassment, under section 653m; and violation of order enjoining harassment under section 273.6.
Under the Stalking statute, 646.9, to “harass” means to engage in a knowing and willful “course of conduct,” without a legitimate or lawful purpose, that is focused on a specific and identifiable person(s) which “seriously alarms, annoys, torments, or terrorizes” that person.  Other courts have said to “harasses” involves a course of conduct directed at a person that would normally result in alarming, annoying, or tormenting someone.
A “course of conduct” means at least two or more acts over a discernable period no matter how short which shows a consistency of purpose and plan. 
An “immediate family member” would include a spouse, a parent, a child, or other close relative, or any other person who regularly resides in the household or has done so within the preceding 6 months.
The term “credible threat” is a threat that is verbal, written, or through an “electronic communication device,” or a combination of all of these and is suggested or implied by a pattern of conduct. The threat places a person in reasonable fear of serious injury, or that of his or her family. It must be made with the “apparent” ability to carry it out. That a person who makes the threat is in custody when the threat is made is not a defense.  The threat does not require proof it can be accomplished, only that it is made with the required intent, and necessary effect on the victim.
 People v. Heilman (1994) 25 C.A.4th 391 , 398, 30 C.R.2d 422; People v. Halgren (1996) 52 C.A.4th 1223, 1229, 1231, 61 C.R.2d 176; People v. Falck (1997) 52 C.A.4th 287, 293, 60 C.R.2d 624; People v. Borrelli (2000) 77 C.A.4th 703, 712, 91 C.R.2d 851.
 People v. Zavala (2005) 130C.A.4th 758, 767, 30 C.R.3d.