The International Earth Science Olympiad (IESO), one of the twelve International Science Olympiads, is an annual competition for secondary school students that test their abilities in disciplines such as geology, meteorology, environmental science, and terrestrial astronomy. Students who are winners of the respective national competitions are invited to participate in the IESO, and all interested countries are encouraged to contribute to the IESO.

It is one of the major activities of the International Geoscience Education Organization - IGEO that aims at raising student interest in and public awareness of Earth sciences, as well as to enhance Earth science learning of students.

All major areas of Earth Sciences, including geology, geophysics, meteorology, oceanography, astronomy, and environmental sciences, are considered for selecting topics for the competition.

The International competition consists of a theoretical and a practical examination. The written examination includes problems which are developed to measure the participants' robust knowledge and understanding in Earth science areas.

Usually, last week of September every year.

The practical examination consists of tasks which are designed to assess participants' abilities to carry out scientific investigations in earth science inquiries. Participants are allowed to bring non-programmable calculators for the examinations. Sometimes special tool are provides as telescopes, geology compass, meteorological instruments and so on.

Each team consists of up to four competing students, an alternate, and mentors. The mentors must be specialists in Earth science and/or Earth science education and capable of serving as members of the International Jury. The official language of the competition is English, and the mentors must also translate for their teams from their native language. Students qualify to attend the IESO by winning national Earth science competitions in their home countries.

The top twenty or so, students who qualify the entrance test for IESO are called for the training camp whose duration is about 20 days. On the basis of performance of these students the final team is selected which represents the particular country at the International Competition.