How many component libraries should we have ideally? Pros and Cons?

In my three years of hands-on experience with design systems, I’ve experimented with each of the approaches you’ve outlined here. When I first started, I leaned towards a separate library for each component. My thought was that this would offer greater granularity and better organization. However, the reality was quite the opposite. The overhead in managing multiple libraries started consuming a significant amount of time. Every time a change was made to a common variable like color or typography, propagating that change across multiple libraries became a herculean task.

My next move was to option 3, where I categorized components into a handful of libraries based on their use case or object type. This felt like a happy medium, with a more manageable number of libraries and logical groupings that made components easier to find. But even then, there were some challenges around redundancy and reusability.

Fast-forward to today, and what I’ve settled on is actually a hybrid between options 2 and 3. This approach leverages the best of both worlds. By having centralized libraries and external libraries for not-in-context published projects (ex. iOs 17 design system) , I’ve drastically reduced the overhead in components management. I don’t need to jump between multiple files or worry about inconsistencies. At the same time, by using variables, I’ve been able to introduce a level of flexibility that almost mimics having separate libraries. For example, in our multi-brand design system, variables are defined at the “primary” level, which then branches out into specific brand implementations into another project for a sub-brand. This makes it easier to manage changes across multiple brands without sacrificing the specificity that a separate library for each would offer.

Thanks, really valuable perspective. I think we are settling on attempting to have a single library, but if it gets too large, we will decide on the policy for how to split the library ahead of time so we can prepare for it.