Things start getting more interesting and tangible when we start combining atoms together. Molecules are groups of atoms bonded together and are the smallest fundamental units of a compound. These molecules take on their own properties and serve as the backbone of our design systems.

For example, a form label, input or button aren’t too useful by themselves, but combine them together as a form and now they can actually do something together.

Building up to molecules from atoms encourages a “do one thing and do it well” mentality. While molecules can be complex, as a rule of thumb they are relatively simple combinations of atoms built for reuse.