Catalyst is becoming one of the most important components in Apache Spark, as it underpins all the major new APIs in Spark 2.0, from DataFrames, Datasets, to streaming. At its core, Catalyst is a general library for manipulating trees. Based on this library, we have built a modular compiler frontend for Spark, including a query analyzer, optimizer, and an execution planner. In this talk, I will first introduce the concepts of Catalyst trees, followed by major features that were added in order to support Spark’s powerful API abstractions. Audience will walk away with a deeper understanding of how Spark 2.0 works under the hood.