This document discusses NoSQL databases as an alternative to relational databases. It provides background on new requirements from web companies that led to the rise of NoSQL, such as high availability, scalability, and flexibility in data structures. Various NoSQL database models are presented, including key-value stores, document databases, and graph databases. The document highlights tradeoffs between consistency, availability, and partition tolerance based on Brewer's CAP theorem. Examples of popular NoSQL databases like Dynamo, Cassandra, and Neo4J are also mentioned.