Until 2016/17, the number of studies at Austrian public universities increased for many years. Since then, this trend reversed as the number of new students decreased noticeably. The aim of this study is to identify possible factors influencing the development of student numbers. We use different data sources to estimate the influence of a selection of factors on the number of commenced and active studies at public universities in recent years, namely demographic development, the rate of high school graduation, the probability of starting an academic study after graduating from high school, multiple enrollment, admission procedures, the expansion of other higher education sectors, Austrian students abroad, and business cycles.