The hair follicle is a continually regenerating and yet complex organ, which is patterned and re-patterned throughout life. Evidence suggests that epidermal hair follicle patterning and regeneration is maintained by signals from the underlying mesenchyme, the dermal papilla. Despite the essentiality of the dermal papilla, the signals required for its development are not well understood and as yet the mechanisms by which the dermal papilla regulates hair growth remains to be determined. We propose that the transcription factor Sox18 regulates dermal papilla signalling to mediate hair follicle growth. Firstly, to address this hypothesis, we used Sox18-GCre transgenic mice to analyse Sox18 expression in the developing dermal papilla and identified that Sox18 is expressed during early dermal papilla formation in all hair follicles types, in a tightly regulated temporal pattern. Secondly, using the dominant negative Sox18RaOP mouse model, we showed that Sox18/SoxF is in fact required for dermal papilla specification and is therefore an essential mesenchymal regulator of hair follicle development. We have also identified a number of novel transcriptional targets of Sox18, and are currently investigating their role in dermal papilla regulation of hair growth. Overall, with these models, we identified that Sox18/SoxF are crucial for dermal papilla specification and maintain signals in the dermal papilla required for induction of growth and patterning in the neighbouring epidermal hair follicle compartment. These results identify a novel mechanism by which complex tissue patterning in the hair follicle is achieved by the Sox18/SoxF mediated regulation of signaling in the associated dermal papilla.