OTRS, an initialism for Open-source Ticket Request System, is a free and open-source trouble ticket system software package that a company, organization, or other entity can use to assign tickets to incoming queries and track further communications about them. It is a means of managing incoming inquiries, complaints, support requests, defect reports, and other communications.

The Open-source Ticket Request System (OTRS) is more than a mailing list notification system for ticket requests. Every ticket generated by the system has persistence or “history” showing what happened to the ticket within its life cycle. OTRS has the ability to merge multiple requests about the same incident, thus making it possible to work on an incident rather than on singular requests. It is a multiuser system which means that multiple agents may work simultaneously on the tickets in OTRS, reading the incoming messages, bringing them in order, and answering them. It is highly scalable, capable of handling thousands of tickets per day and a nearly unlimited number of simultaneously working agents.