Atmosphere Independent Power has been with us for more than 80 years but there is still an impressive amount of development work going on. The more so after nuclear propulsion set an unattainable goal that can therefore not be emulated by the most advanced concepts. Even so conventional AIP submarines, small and large, can profit from operational advantages depending on the specific system. Hence the question remains what to choose from a variety of options. This overview is intended to provide a background on what is available “off-the-shelf” and what can be expected from on-going development even if today’s naval architect has to wait for the promises to become true. The present paper provides an overview of the options and the impact they have on the submarine design under consideration. Apart from Closed Cycle Diesel and Stirling systems also Fuel Cell systems with stored or reformed H2 are reviewed. In addition the performance of advanced batteries is included as an alternative to AIP