In this exploration of the globalization of science curricula, a coding exercise, cluster analysis and discriminant analysis of twenty years of TIMSS data were used to answer three research questions: (1) Have there been changes in intended science curricula over the last 20 years? (2) If changes do exist, do they support the hypothesis that science curricula are becoming increasingly similar across countries? (3) Are there groups of countries where curricula are increasingly similar; can the basis of an international core curriculum be identified? The analysis provides strong evidence to suggest that there have been changes to countries' intended science curricula. The coding exercise found that all countries in the analysis had made changes to their intended curricula, although the extent of curricular changes varied considerably between countries. Cluster and discriminant analyses showed that over time there was a tendency for countries to cluster into one particular grouping based on responses to the TIMSS curriculum questionnaire. The number of TIMSS science topics that could be considered core to the curricula of the majority of participating countries increased over time, particularly at Grade 4, suggesting that science curricula are becoming increasingly similar across countries. Among the two groups of countries identified by the cluster and discriminant analyses, there was a clear tendency for one group to include a wider science curriculum encompassing a greater range of science topics than the other group. At Grade 8 the results strongly suggest that there has been convergence in science curricula over time. In terms of whether an international core curriculum can be identified, there are some TIMSS science topics which could be considered core to the curricula of most countries. Assessment is likely to play an important role, as high-stakes assessment is likely to influence science curricula and what is taught in schools. Keywords Core science curriculum Á Curriculum change Á Curriculum convergence Á Curriculum development Á Globalization Á Science curriculum Science education Á Trends in Mathematics and Science Study (TIMSS)