Composability is a system design principle, specifically the ability to mix and match software components (such as Lego blocks). Each software component needs to be written only once, after which it can simply be reused. This is similar to an interest in compound interest in finance or Moore's Law in computing - some of the most powerful known economic forces - because it can unleash exponential power.

In their most powerful form, composability and interoperability are possible across a wide range of software stacks. Decentralized finance or DeFi is an example of this powerful form. Anyone can tweak, recycle, change or import existing code. Not only that, but developers can build real-time programs - such as Compound's lending protocols or Uniswap's automated market-making transactions - side-by-side in the memory of a shared virtual computer (ethereum) at their leisure. By combining powerful new elements such as property rights, identity and ownership, builders can create entirely new experiences.