Accessibility is important for three main reasons: (1) It is the right thing to do to provide equal access to information and functionality for all users, including those with disabilities, (2) It is required by law, such as Section 508 which mandates accessibility of electronic resources for U.S. federal agencies, and (3) It benefits all users by creating easier to use, more intuitive interfaces and reaching a wider audience. The document discusses what accessibility means, why it is important, examples of disabilities and assistive technologies, principles of accessibility like making content perceivable, operable, understandable and robust, common accessibility problems to avoid, and resources for testing and learning more.