The talk covers how Elasticsearch, Lucene and to some extent search engines in general actually work under the hood. We'll start at the "bottom" (or close enough!) of the many abstraction levels, and gradually move upwards towards the user-visible layers, studying the various internal data structures and behaviors as we ascend. Elasticsearch provides APIs that are very easy to use, and it will get you started and take you far without much effort. However, to get the most of it, it helps to have some knowledge about the underlying algorithms and data structures. This understanding enables you to make full use of its substantial set of features such that you can improve your users search experiences, while at the same time keep your systems performant, reliable and updated in (near) real time.