A Private Detective or Private Investigator (PI) is a person who conducts investigations, usually for a private citizen, business, or organization. They also can work for attorneys in civil cases or criminal cases on behalf of a defense attorney or a client. Many Private Investigators work for insurance companies to investigate suspicious insurance claims for that company. Some Private Investigators also are hired to search for evidence of adultery or other illegal conduct within a marriage to establish grounds for divorce or child custody. Within the Private Investigation Industry nation wide adultery or other "socially unexcitable behavior" by spouses and partners is one of the most profitable activities investigators undertake. Private Detectives also conduct process serves, background checks, skip tracing, and locating of missing persons. Many agencies across the country specialize in one particular field of expertise. For example, some PI agencies deal only in skip tracing, others may specialize in surveillance, and still others may specialize in bug detection which is the locating and disposing of unwanted forms of electronic surveillance often found in corporate espionage or personal eves dropping cases. Some of the other many specialties a PI might have is Fraud Investigations, Personal Security or Bodyguard details, and Computer Forensics to name a few.

Private Detectives and Private Investigators often work irregular hours due to of the needs of there case which require them to conduct surveillance and contact people who may or may not be available during normal working hours. Early morning, evening, weekend, and holiday work is common. Most Private Detectives and Private Investigators spend a majority of there time away from their offices conducting interviews or surveillance, but some work in their office most of the day conducting computer searches and making phone calls. Those who have their own agencies and employ other investigators may work primarily in an office and have normal business hours. Sometimes an investigation calls for the investigator to be armed, such as certain bodyguard assignments for corporate or celebrity clients. Detectives and investigators who carry handguns must be licensed by the appropriate authority in most cases to carry a firearm on duty. In most cases, however, a weapon is not necessary, because the purpose of the work is gathering information and not law enforcement or criminal apprehension.

Most states require that Private Investigators be licensed. Some Private Detectives are former police officers or former military, although many do not have that kind of professional background. Many states have strict laws that govern and regulate the Private Investigation industry in there state. A Private Investigator often works long hours, keeping detailed notes and video for reports to supply to there clients and often spend most of there time in the field conducting surveillance related work. Many Private Detectives have college degrees or have taken legal or criminal investigation related courses to better prepare themselves for there particular field of investigation. Private Detectives and Private Investigators typically have previous experience in other occupations that prepares them for there career as a Private Investigator. Some previously worked for insurance or collections companies, in the private security industry, or as paralegals. Many investigators enter the field after serving in law enforcement, the military, government auditing and investigative positions, or federal intelligence jobs, which makes them an expert in that field of investigation due to there experience.

Former law enforcement officers, military investigators, and government agents, often become Private Detectives or Private Investigators, others from such fields as finance, accounting, commercial credit, investigative reporting, insurance, law, etc. These individuals often can apply their prior work experience in a related investigative specialty and be considered experts in there field.

A background in subjects such as criminal justice and police science can be helpful to anyone interested in Private Detectives and Private Investigators employment. Most corporate investigators require having a bachelor’s degree, preferably in a business-related field. Some corporate investigators have a master’s degree in business administration or a law degree, while still others are CPAs. Corporate investigators hired by large companies may receive formal training from their employers on business practices, management structure, and various finance-related topics. The screening process for potential employees typically includes a background check for a criminal history.

The majority of States require private detectives and Private Investigators to be licensed in there state. Licensing requirements vary, dramatically however. Seven states (Alabama, Alaska, Colorado, Idaho, Mississippi, Missouri, and South Dakota) have no statewide licensing requirements, other states have very few requirements, and many more states have very stringent regulations. A growing number of states are enacting mandatory training programs for private detectives and investigators. For example, the Bureau of Security and Investigative Services of the California Department of Consumer Affairs requires private investigators to be 18 years of age or older, have a combination of education in police science, criminal law, or justice and experience equaling 3 years (6,000 hours) of investigative experience, pass a criminal history background check by the California Department of Justice and the FBI (in most States, convicted felons cannot be issued a license), and receive a qualifying score on a two-hour written examination covering laws and regulations. There are additional requirements for a firearms permit.

Most private-detective agencies are small, with little room for advancement due to not more than one to three Private Investigators in the Firm. Usually, there are no defined ranks or steps, so advancement takes the form of increases in salary and assignment status. Many detectives and investigators work for detective agencies at the beginning of their careers and, after a few years, start their own Agency after receiving the necessary experience. Corporate and legal investigators may rise to supervisor or manager of the security or investigations department.