Cytoplasmic mRNA localization is an important biological strategy for establishing cell and developmental polarity in a variety of organisms and cell types. In diverse examples including oocytes, fibroblasts and neurons, mRNA localization results in spatially restricted gene expression through local protein synthesis. In Xenopus laevis oocytes, maternal mRNAs are transported to the vegetal hemisphere of developing oocytes where their local translation is critical for proper embryonic patterning. Motor-based vegetal transport of such mRNAs relies on the assembly of RNP transport cargos, a conserved feature of RNA localization pathways. However, the molecular and physical nature of these structures has remained largely unknown. Our recent work has revealed that that that the RNA cargos are phase-separated biomolecular condensates that contain a solid- or gel-like RNA phase and a dynamic protein phase.