The International Astronomy Olympiad (IAO) was established and its foundation were published by the Euro-Asian Astronomical Society (EAAS), in order to spread astronomical knowledge, promote international cooperation in astronomical education area, and recognize the importance of astronomy in far-reaching field of science and human culture. In 1996, the first IAO was held at the Special Astrophysical Observatory (SAO) of the Russian Academy of sciences (RAS) located in the north Caucasus of Russia. Since then, it has been held every year. Here, we will describe the present status of the International Astronomy Olympiad, its major results by year, related institutions, organizations, and the main regulations regarding its operation. In order to measure the levels of scientific knowledge and thinking abilities, we develop a rubric to analyze the characteristics of problems in the IAO with regards to cognitive aspects of scientific inquiry. These problems require high levels of content knowledge and scientific method knowledge. Also high order thinking abilities and high levels of convergent thinking skills, instead of divergent, are needed to solve these problems. Thus, the problems presented are set a high difficulty. Through this analysis, we can understand main purpose of the International Astronomy Olympiad and explore the future direction of the Korea Astronomy Olympiad.