Mobile apps have grown fast since 2008, and mobile app global revenues amounted to 69.7 billion U.S. dollars in 2015. Hence, knowledge of mobile apps is of importance to mobile app developers, mobile app platform producers, and consumers following its size and expected growth. Mobile app downloads, i.e. how many times an app has been downloaded, are often claimed to reflect an app's popularity. A systematic literature review is conducted to identify what are the determinants of mobile app downloads, and to give guidance for future research. A total of 27 articles are selected as the final sample based on searches in four scientific databases. The selected articles identify a diverse set of determinants. In order to present results of selected articles in a more systematic way, I analyse the results of selected articles by three themes, which are consumers' intention, app developer strategy, and platform information (e.g. ratings, reviews and ranking), according to their purposes or research questions. The determinants of mobile app downloads summarized from the selected literatures are: perceived usefulness, perceived enjoyment, peer information, perceived ease of use, user interests, perceived risk, freemium strategy, advertisement, price, app selling category, app type, consumer ratings (valence, volume and variance), character of consumer reviews, top list ranking, etc. The dominant method among these articles is regression analysis. The review also shows that there is a need for better theoretical explanation to why consumers download mobile apps. Different robustness checks by econometric models can be done to test different determinants of mobile app downloads in further studies. Determinants from mobile app developers and platform information are less studied in previous researches, thus mobile app business strategy, consumer ratings and reviews, and mobile app categories need to be explored deeper in future researches. The relative importance of different determinants under different circumstances need to be investigated in more depth in future research.