We present a summary of the extensive problems posed by the curious abundance correlations seen in stars in Galactic globular clusters. We discuss three scenarios, and conclude that only one seems to be consistent with the observations. Even this is still rather unsatisfying from many viewpoints. We determine the kind of nucleosynthesis required and discuss AGB stars as the possible source. Some calculations seem to rule out AGB stars and others seem to favour them. The reasons for the differences are discussed. No satisfying conclusion is reached!