Plasmids are circular double-stranded DNA and have been the workhorse of molecular biology. They can also be adopted by more complex organisms to influence how their cells behave. Importantly, this means they can be leveraged to study intricate molecular networks, and gene-function relationships, and hold promise as therapeutic devices. Thus, the ability to deliver and control their activity will not only advance their utility in research fields such as developmental and molecular biology but also expedite their translation to clinical settings. In this regard, light is a convenient stimulus as it is non-invasive, and its properties and application can be adjusted to minimise cellular damage. However, examples of light-controlled plasmid are limited, with the majority displaying poor light-dependent activation, or necessitating specific sequences that limit their use. This thesis outlines the development of a general strategy to deliver light-activated plasmids. This approach relied on photoblocking groups placed at the promoter, which could be removed in response to UV light. This strategy was used to control two ubiquitous bacterial and mammalian promoters. Cell-free reactions with the T7 promoter could be tightly repressed until the UV stimulus was applied. Likewise, light-regulated transcription and translation from the CMV promoter were also demonstrated in mammalian cells, although the photomodulation efficiency was more modest. However, this strategy failed to work on the tac and Sp6 promoters, which is likely due to the difference in binding interactions between the promoter and their cognate RNA polymerase partner. Thus, although this strategy worked well for the T7 promoter in cell-free reactions, the promoter dependency would mean that optimisation is required when the strategy is adopted to photocage alternative promoters. Furthermore, an outstanding challenge needs to be overcome before plasmids can be used for therapy: the inefficient delivery of large negatively charged molecules into cells. Initial studies in this regard were made, and suggestions to enable plasmid delivery were outlined. Unlike previous examples, this technology has the potential to be sequence agnostic, meaning it could be adaptable to any plasmid, greatly expanding its scope.