This document provides an overview of Apache Drill, an open source SQL query engine for analysis of both structured and unstructured data. It discusses how Drill allows for schema-free querying of data stored in Hadoop, NoSQL databases and other data sources using SQL. The document outlines some key features of Drill, such as its flexible data model, ability to discover schemas on the fly, and distributed execution architecture. It also presents examples of using Drill to analyze real-world data from sources like HDFS, MongoDB and more.