This document provides an overview and introduction to MongoDB. It discusses how new types of applications, data, volumes, development methods and architectures necessitated new database technologies like NoSQL. It then defines MongoDB and describes its features, including using documents to store data, dynamic schemas, querying capabilities, indexing, auto-sharding for scalability, replication for availability, and using memory for performance. Use cases are presented for companies like Foursquare and Craigslist that have migrated large volumes of data and traffic to MongoDB to gain benefits like flexibility, scalability, availability and ease of use over traditional relational database systems.