Techniques for dietary and palaeoclimate reconstruction based on stable isotope ratios in the mineral phase of calcified tissues show great promise, but their pathways of development have not been smooth. Two separate trajectories, based on the phosphate and carbonate compartments respectively, have been pursued,usually by different protagonists. There are parallels in the development of these two ‘fields’, however. A fundamental commonality lies in the constraints imposed by the nature of calcified tissue minerals and by diagenesis, although realization of their significance has perhaps been slower amongst phosphate practitioners. In this paper I show how incomplete understanding of the nature of biological apatites, coupled with our often limited understanding of natural variability in carbon and oxygen isotopes in animals, has impeded progress in both areas. Nevertheless, enormous strides have been taken over the past two or so decades. Some of the important milestones in the development of these two techniques are chronicled. With emerging understanding of oxygen isotope variation in mammalian biological apatites and their consequences for behavioural and palaeoclimate interpretations, the two fields are drawing closer together.