This document provides an overview of NoSQL databases, including a brief history, classifications, pros and cons of usage, and trends. It discusses how NoSQL technologies originated from distributed computing needs and were driven by scalability, parallelization, and costs. Major classifications of NoSQL databases are described as column-oriented stores, key-value stores, document stores, and graph databases. Examples like MongoDB, Cassandra, and Neo4j are outlined. Both benefits and limitations of NoSQL are presented. Emerging trends around SQL access and adoption of Hadoop are also noted.