Internships for professional careers are similar in some ways but not as rigorous as apprenticeships for professions, trade and vocational jobs,[3] but the lack of standardisation and oversight leaves the term open to broad interpretation.[4][5] Interns may be college or university students, high school students, or post-graduate adults. These positions may be paid or unpaid and are usually temporary.

Generally, an internship consists of an exchange of services for experience between the student and an organization. Students can also use an internship to determine if they have an interest in a particular career, to create a network of contacts, to acquire a recommendation letter to add to their curriculum vitae, or to gain school credit. Some interns find permanent, paid employment with the organizations for which they worked upon completion of the internship. This can be a significant benefit to the employer as experienced interns often need little or no training when they begin regular employment. It also helps an employer in gauging a student’s aptitude, since grade inflation has undermined the reliability of academic grades.[6] Unlike a trainee program, employment at the completion of an internship is not guaranteed.

Internships exist in a wide variety of industries and settings. An internship may be paid, unpaid, or partially paid (in the form of a stipend). Stipends are typically a fixed amount of money that is paid out on a regular basis. Usually, interns that are paid through stipends are paid on a monthly basis. Paid internships are common in professional fields including medicine, architecture, science, engineering, law, business (especially accounting and finance), technology, and advertising. Non-profit charities and think tanks often have unpaid, volunteer positions. Internships may be part-time or full-time. A typical internship lasts between one and four months,^[7] but can be shorter or longer, depending on the organisation involved. The act of job shadowing may also constitute interning.

The two primary types of internships that exist in the United States are:

• Work experience: Most often this is in the second or third year of the school period. The placement can be from two months to one full school year. During this period, the student is expected to use the things they have learned in school and put them into practice. This way the student gains work experience in their field of study. The gained experience will be helpful to finish the final year of study.
• Research (graduation) or dissertation: This is mostly done by students who are in their final year. With this kind of internship a student does research for a particular company. The company can have something that they feel they need to improve, or the student can choose a topic within the company themselves. The results of the research study will be put in a report and often will have to be presented.

European internships are popular among non-Europeans in order to gain international exposure on one’s résumé and for foreign language improvement, although they may be unpaid.

Another type of internship growing in popularity is the virtual internship, in which the intern works remotely, and is not physically present at the job location. It provides the capacity to gain job experience without the conventional requirement of being physically present in an office. The internship is conducted via virtual means, such as phone, email, and web communication. Virtual interns generally have the opportunity to work at their own pace.