This document provides an overview of ArcGIS extensions that can expand the capabilities of ArcGIS software. It describes several extensions including ArcGIS Spatial Analyst, ArcGIS 3D Analyst, ArcGIS Geostatistical Analyst, ArcGIS Network Analyst, and ArcGIS Schematics. These extensions allow for advanced spatial analysis, 3D visualization and surface generation, statistical analysis of spatial data, network-based analysis including routing and service areas, and automation of schematic representations. The extensions can be used with ArcGIS Desktop as well as ArcGIS Server and ArcGIS Engine.