Database Management Systems is a core subject which explains how data is designed to develop computer applications. It mainly covers how data is stored, organized and retrieved for commercial applications such as railway reservation systems and banking applications. The book Database Management Systems 2nd edition has been written for MCA 1st year students of Abdul Kalam Technical University. The book has been written according to the syllabus of the subject Database Systems and concepts have been explained well through the help of examples and diagrams. The book contains Introduction to Databases, Entity Relationship diagrams, Relational Algebra, Structured Query Language and PL/SQL. Also it explains Functional Dependencies and Normalization. It covers Transaction Processing, Concurrency Control Management, Distributed Databases, NoSQL and MongoDB. Solved Examples of ER diagrams, SQL Queries, Queries of Relational Algebra, Functional Dependency Problems, Transaction Problems and MongoDB Queries are provided at the end of the book so that students gain better understanding of the database concepts. The book will be beneficial to students of other universities as well who are studying this subject. This book is the second edition of Database Management Systems book which has appended NoSQL concepts and Introduction to MongoDB with queries.