Elasticsearch is a search server based on Apache Lucene that can store and search JSON documents. Its distributed architecture allows for the storage of very large amounts of data. In addition to full-text content, structured data can also be managed and easily grouped and queried with aggregations. Documents, search queries, and administrative tasks are formulated in JSON and exchanged via HTTP or through the Java API. The book introduces the use of Elasticsearch through a continuous example. After an introductory chapter that builds a classic search application from scratch, subsequent chapters delve into different aspects in more detail. Among other topics, the following areas are addressed: handling text, relevance in search results, indexing options, and data distribution.