In today’s Web world, we see that the data production has been enormous, and organizations also face tough challenge in terms of processing, analyzing, and storing big data. The issue faced by organizations was how to manage the data which was not in a fixed schema which is also called unstructured data. For example, data being collected from social media network. Because of the data format, Relational Database has some limitations where NoSQL comes-into the picture which offers highly flexible and horizontally scalable solution to store structured, semi-structured and unstructured data. The process of data storage in NoSQL is in form of key-value pairs which offer better availability and high throughput performance in terms of processing queries. Since it does not require to have a fixed Schema, we can customize it as per user requirements. The unstructured database has existed since late 1960’s but the need of such database never arose until the Web 2.0 companies needed it. It was when companies like Facebook, Google and Amazon.com wanted a database which could store the data produced by their web-based applications. NoSQL are also known as Not only SQL or No SQL database because it does not store data into a form of relational tables. The increasing trend of different type of applications and data has caused the developers to reevaluate how data is stored and managed. The behavior of today’s data needs a technology which provides scalable, flexible solution to manage their huge amount of unstructured data which are difficult, and sometimes impossible to be managed by relational database models (such as Oracle, MySQL, SQL Server, and IBM DB2). This problem caused many to divert their interest towards NoSQL Database for flexibility. NoSQL (not only SQL) were introduced to handle unstructured and continuous growth of unstructured data. In this paper, we will go through Introduction to DBMS, RDBMS and NoSQL database, NoSQL Database categories, and will be covering an example of NoSQL Database (MongoDB) briefly.