This book is a good introduction of Graph Database Systems (GDBS) in general and for neo4j as an example. It describes the basic concepts of graph databases and the differences to Relational Database Systems (RDBMS). Therefore, it is readable for people with a basic / good understanding of RDBMS. The book introduces the query language Cypher, explains how data is organized on disk and how the API can be used in Java (latter both for neo4j). Since the development of neo4j is still heavily in progress, the book is (only) a starting point for the work with GDBS. All other specific and necessary information can / need to be taken from the comprehensive online documentation.