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 Massachusetts, private investigators are regulated under state law and must be licensed to legally conduct surveillance and investigations. The licensing process is overseen by the Massachusetts State Police Certification Unit, and applicants must meet certain requirements, including a background check, experience or education in the field, and passing an examination. When hired during a divorce process to investigate suspicions of adultery or other improper behavior, private investigators must adhere to legal methods of surveillance. This means they can observe and collect evidence in public places where there is no expectation of privacy. However, they must not engage in illegal activities such as trespassing, wiretapping without consent, or harassment. The evidence gathered by private investigators can be used in divorce proceedings to support claims of adultery or other misconduct, which may affect alimony, asset division, or child custody decisions. It's important to note that while Massachusetts is a 'no-fault' divorce state, evidence of fault, such as adultery, can still be relevant in certain aspects of the divorce settlement.