Memoize is a package for externalization of graphics and memoization of compilation results in general, allowing the author to reuse the results of compilation-intensive code. Memoize induces very little overhead, as all externalized graphics is produced in a single compilation. It features automatic recompilation upon the change of code or user-adjustable context, and automatic externalization of TikZ pictures and Forest trees, easily extensible to other commands and environments. Furthermore, Memoize supports cross-referencing, TikZ overlays and Beamer.