Perivascular fibroblasts (PVFs) are fibroblast-like cells located between astrocyte endfeet and vascular smooth muscle cells (vSMCs), present on arterioles and venules in the brain. PVFs are a recognized component of the neurovascular unit that supports the central nervous system, but their development is not well understood. Now, Julie Siegenthaler and colleagues chart the emergence and integration of PVFs into the neurovascular unit during mouse brain development. The authors use Col1a1-GFP transgenic mice, combined with immunofluorescence, to label PVFs to show that PVFs emerge on the cerebral cortical vessels between postnatal day (P) 5 and P14, following the establishment of vSMCs and astrocyte endfeet, and concurrent with perivascular macrophage development. Through sophisticated genetic lineage-tracing experiments, such as Brainbow, they show that PVFs originate from fibroblasts in the leptomeninges (the inner two membranes that protect the brain) at embryonic stages. Furthermore, clonal PVFs cluster on vessels in non-overlapping domains, potentially reflecting the temporal emergence and migration of individual PVFs. Finally, using whole-mount clearing methods and two-photon imaging, the researchers show that PVFs enter the brain via penetrating vessels at P5, before migrating, proliferating and refining their position on target vessels. Together, these data provide a thorough morphological and statistical analysis of PVF development.