This document provides an overview of natural user interface (NUI) research as it relates to human-computer interaction (HCI). It defines HCI and notes that NUI is an emerging paradigm that aims to make interfaces invisible through natural motions, gestures, and interactions. The document outlines relevant areas of HCI including computer science, behavioral sciences, and design. It discusses NUI focus areas like touch, vision, speech and technologies like touchscreens, voice input, and augmented reality. Examples of NUI applications are also presented. Challenges with NUI include the currently high costs of developing the specialized technology.