IBO is one of the international science Olympiads. The first International Biology Olympiad took place at Olomouc, Czechoslovakia in 1990. The latest edition of IBO took place recently at Aarhus, Denmark.
All participating countries send the four winners of their National Biology Olympiad to the IBO, accompanied by usually one team leader and two observers/jurors.
The competition itself is composed of a theoretical and practical element. The theory exams cover a wide range of Biology: Cell Biology, Molecular Biology, Plant Anatomy and Physiology, Animal Anatomy and Physiology, Ethology, Genetics and Evolution, Ecology, and Biosystematics. The marks are scaled so that the theory and practical components each have a weighting of about fifty percent.
I've compiled all the past IBO problems (Some also contain solutions). You can download the compiled version here.