A private investigator or private detective is a person who secretly follows and observes persons in public places for the purpose of witnessing behavior and collecting evidence of any illegal or improper activities (photos, videos, etc.). During the divorce process a spouse who suspects their spouse of cheating (adultery) or other improper or illegal behavior may hire a private investigator to follow or “tail” the other spouse.

In Maine, private investigators are regulated under state law and must be licensed to legally conduct surveillance and investigative work. The Maine Department of Public Safety is responsible for the licensing of private investigators, and applicants must meet certain requirements, including passing a background check and having a certain amount of investigative experience or equivalent law enforcement experience. When hired during a divorce process to investigate suspicions of adultery or other improper behavior, private investigators must operate within the bounds of the law. This means they must not trespass on private property, engage in illegal wiretapping, or otherwise violate privacy laws. Evidence gathered legally by a private investigator can be used in court proceedings, including divorce cases. However, it is important to note that Maine is a 'no-fault' divorce state, meaning that evidence of adultery may not necessarily impact the outcome of the divorce proceedings as significantly as in some other states. An attorney can provide guidance on how evidence obtained by a private investigator might be used in a specific divorce case.