Duolingo is a free language learning website and app that uses a gamified approach to teach languages.  Through a partnership with the Klingon Language Institute their Klingon language learning course is one of the best online options for learning Klingon for English speakers.  The lessons include translation and listening exercises with characters who read sentences for you and quiz you.  The software adapts to individual users and the software algorithms try to determine which sentences will help each learner learn the best.

The Klingon course started development in 2014 after KLI member Felix Malmenbeck volunteered to work on Duolingo's Language Incubator.  A few other members helped in various ways, most notably Phillip Newton and Jeremy Cowan.  The course was released March 15, 2018.  After the course was released, Duolingo and the KLI formed a partnership to maintain and improve the course.  Robyn Stewart, Alan Anderson, and Juliana Bukoski were brought on as contractors to help complete the course audio and improve the beginning of the course.

You can register for the web version of the course for free at Duolingo Learn Klingon.  The course is also available on both iOS and Android devices.  In early 2022 Duolingo decided to pause development on many of the smaller courses to focus resources on larger courses and on software and feature development, but the Klingon course is able to run without human maintenance and remains available for free. It is hoped that they may return to staffing some of the smaller courses in the future and the KLI will be able to actively improve the course again.

Note that while access to all parts of the Duolingo Klingon course is free, there are ads and daily limits.  Users can purchase Super Duolingo to remove the ad and the daily limits.  Duolingo also offers a subscription level called Duolingo Max, but this subscription does not add any new features for the Klingon course.  The KLI recommends that users of the Duolingo course also purchase a digital or print copy of The Klingon Dictionary by Marc Okrand to use as a reference.

Originally "Tips and Notes" were created by the contributors for the Duolingo Klingon language course, but Duolingo never fully implemented the "Tips and Notes" since the software is designed to teach by examples rather than through explanations.  However, Klingon is different enough from English that it can be hard to learn without explanations. Thus the KLI has made these notes available to help guide learners through the various course units.  Following are links to the pages containing the Tips for each Unit of the course.