The 21st century, along with the 4.0 industrial era, has witnessed the creation and development of many software and apps for educational purposes. Among all the apps and software introduced, Duolingo has been proven to be a useful and effective tool to learn vocabulary. This research aims to review some theories related to the definition of learning media and the importance of vocabulary inlanguage teaching and learning process
therefore, suggests some ways to use Duoling as a learning tool to improve students’ vocabulary.