This document introduces human-computer interaction (HCI). It defines HCI as a field that deals with humans, computers, and the interaction between them. The objective of HCI is to design interactive systems that support people in their everyday lives. HCI considers both the user and the computer, where the user can be an individual or group, and the computer encompasses any technology from desktops to embedded systems. Interaction in HCI refers to any communication between the user and computer, whether direct or indirect. The document provides a formal definition of HCI and discusses elements of a successful HCI product.