The diversification of cropping systems encompasses different strategies that may help maintain or enhance the sustainability of agriculture. Thousands of experiments have been carried out around the world since almost five decades to evaluate and compare the performances of various diversification strategies in a wide array of agroecosystems and climates. Although these analyses have been synthesized in a growing number of meta-analyses, the information remains somewhat fragmented. A multicriteria systematic synthesis of worldwide agricultural diversification is still lacking. Here, we review all meta-analyses conducted on crop diversification strategies and produce a detailed overview of their results and of their quality. We identified and analyzed 99 meta-analyses summarizing the results of more than 3700 agronomic experiments on seven crop diversification strategies. Among these strategies, rotation and associated plant species are dominant in the literature followed by intercropping, agroforestry and landscape heterogeneity. Our analysis reveals that rotation and intercropping are associated with yield increases. Agroforestry systematically induces an improvement of biodiversity and soil quality—in particular soil organic carbon. We show that, regardless of the context, a combination of several diversification strategies outperforms any individual strategy. Our review reveals that a significant knowledge gap remains, in particular regarding water use, farmers' profitability, product quality and production stability. Few meta-analyses investigate the performance of landscape heterogeneity and of systems with species other than cereals and pulses. Additionally, we show that most of the meta-analyses studied cannot be considered fully transparent and reproducible. Their conclusions should therefore be interpreted with caution. Our systematic mapping provides a benchmark to guide and improve the relevance and reliability of future meta-analyses in agronomy.