The author describes the historical background on antiparticles and the experimental work that led to the discovery of the antinucleons. Many of the properties of the antiproton which can be predicted exactly on the basis of Dirac's theory have been verified. The outstanding problem is now to find the other properties which cannot be predicted on the basis of Dirac's theory and a start in this direction has been made. The latest experiments on cross-section measurements and modes of annihilation are described.