This thesis investigates the viability and compatibility of an industrially-mature metal thin film patterning process, that uses flexography printing in vacuum environments, for application to functional organic devices. The integral thermal mechanism of this process, called selective metallization, is modelled, showing its compatibility with functional organics (process temperature <60°C, Al sheet resistance <1.59Ω◻^-1}). The first example of sub-10μm lateral patterning, using this technique, is presented. These results demonstrate that, for this process, the flexography ink transfer defines the pattern quality. The pattern quality of the printed metal is optimised, using custom-built in-vacuum flexography equipment. The pattern quality metrics, quantified using specially developed image analysis code, vary parabolically with printing pressure and diminish with increased printing speeds. A hierarchical phenomenological model of ink transfer is developed, which fits the data well. Optimal printing parameters reduce line edge peak-to-peak roughness to <1/2 nominal pattern gap, enough to remove electrical defects. These optimised printed patterns are used as electrical contacts for organic thin film transistors (OTFTs), as a proof of concept. Device characterisation shows a change in transistor performance, compared to batch-processed Au contacts, resulting from a charge carrier injection layer, MoO_x(x<3), which is necessary for band matching of the organic semiconductor with the high work function Al. Overall, the changes with MoOx thickness and configuration demonstrate selective metallization is compatible with OTFTs, with a contact resistivity of 1Ωcm^-2. To conclude, exploratory results, of selective metallization applied to organic light emitting diodes, and in-vacuum printing of an organic dielectric material, demonstrate the potential wide applicability of in-vacuum flexography.