Natural products (NPs) have been shown to be an extraordinary source of bioactive compounds and three-dimensional complex frameworks that can be useful to produce high-value molecular collections that are able to address "undruggable" and difficult therapeutic targets. Bicyclic acetals are particularly relevant for these purposes, given their key role in several biological interactions and the structural and stereochemical diversity that comes from the many possible ring combinations. To investigate this topological diversity, we have systematically characterized in a systematic and detailed manner fused, spiro and bridged bicyclic acetals in a large set of NPs, highlighting the great potential of bicyclic acetals in Diversity-Oriented Synthesis (DOS). Accordingly, a summary of some recent efforts on the development of acetal-containing small molecule collections through DOS approaches is herein reported.