As humanity works hard to develop tools which enable humans to extract mineral resources in outer space, we have focused in this chapter on the taxation of such activity because we believe that taxing is the only way how to safeguard mining while keeping peace and harmony with any extra-terrestrial civilisations. Concerning the taxation design, we also concentrated on the theories that we consider important aspects in terms of future taxation and assume step by step, i.e. the Fermi paradox, the Drake equation, the Kardashev scale, the planet Earth’s inflation, the US dollar value and the Laffer curve. In our opinion, it is necessary to employ the accounting principle of prudence when exploring outer space since journeys through the universe may intersect with extra-terrestrial civilisations. Should that happen, such civilisations might demand compensation for the property benefits which humans had achieved within their territories. Hence we propose to incorporate this theoretical possibility as early as the taxation design stage, which will lead to a greater level of security when negotiating the allocation of outer space for the future. As a result, we consider, inter alia, three types of space civilisations, extending Semerád’s proposal to include a proportional share as part of the mining tax and subsequent enforcement of compliance.