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Web services rely on caching at nearly every layer of thesystem architecture. Commonly, each cache is implementedand maintained independently by a distinct team and is highlyspecialized to its function. For example, an application-datacache would be independent from a CDN cache. However, thisapproach ignores the difficult challenges that different cachingsystems have in common, greatly increasing the overall effortrequired to deploy, maintain, and scale each cache.This paper presents a different approach to cache devel-opment, successfully employed at Facebook, which extractsa core set of common requirements and functionality fromotherwise disjoint caching systems.CacheLibis a general-purpose caching engine, designed based on experiences witha range of caching use cases at Facebook, that facilitates theeasy development and maintenance of caches. CacheLib wasfirst deployed at Facebook in 2017 and today powers over 70services including CDN, storage, and application-data caches.This paper describes our experiences during the transitionfrom independent, specialized caches to the widespread adop-tion of CacheLib. We explain how the characteristics of pro-duction workloads and use cases at Facebook drove importantdesign decisions. We describe how caches at Facebook haveevolved over time, including the significant benefits seen fromdeploying CacheLib. We also discuss the implications our ex-periences have for future caching design and research.