NoSQL solutions have been created to respond to many issues encountered when dealing with some specific applications, e.g., storage of very large datasets. In fact, traditional RDMS ensure data integrity and transaction consistency. But, this is at the cost of a rigid storage schema and a complex management. Certainly, data integrity and consistency are required in many cases like in financial applications but they are not always needed. The goal of this paper is to establish a precise picture about NoSQL’s evolution and mechanisms as well as the advantages and disadvantages of the main NoSQL data models and frameworks. For this purpose, first, a deep comparison between SQL and NoSQL databases is presented. Many criteria are examined such as: scalability, performance, consistency, security, analytical capabilities and fault-tolerance mechanisms. Second, the four major types of NoSQL databases are defined and compared: key-value stores, document databases, column-oriented databases and graph databases. Third, we compare for each NoSQL data model the main available technical solutions.