This document provides an overview of nanotechnology including definitions, history, and applications. It defines nanotechnology as the design and manipulation of materials at the nanoscale (1-100 nm) to produce novel properties. Nanomaterials are characterized by their small size and increased surface area. The document outlines the bottom-up and top-down approaches to nanotechnology and gives examples of applications in various fields including medicine, computing, and the environment. It specifically discusses applications of nanotechnology for water purification such as detection, filtration membranes, and biofilm removal. The document concludes with noting both the promise and environmental implications of nanotechnology that require further study.