The most common trigger is launching a summer or semester internship program at a startup or growing company, where founders want eager talent but have not thought through whether the FLSA requires pay. A written agreement forces that decision early, before the intern has worked three weeks and a wage claim is already taking shape. The second frequent scenario is a for-profit business taking on a student for academic credit. Credit alone does not make an internship lawfully unpaid, but a role genuinely integrated with a degree program scores well on the primary beneficiary test, and the agreement is where you record that integration.
Nonprofits and charities reach for this document when they want to distinguish a true learning placement from ordinary volunteer help or from a paid junior role. The line is real, and the paperwork keeps it visible. Companies also use an internship agreement when an intern will touch sensitive material, since confidentiality and invention-assignment language belongs in the contract from day one, not in an afterthought email.
Two edge cases legitimize careful drafting. First, the intern who quietly becomes indispensable: once a so-called intern is covering a vacant role, answering customer tickets, or hitting revenue targets, the displacement factor flips against you and the position has effectively become paid employment. Second, the international intern on a J-1, F-1 CPT, or OPT status, where immigration rules layer on top of wage law and the agreement has to satisfy both. Treat the agreement as the moment you classify the role, not as a formality you sign after the fact.