Professional development refers to many types of educational experiences related to an individual's work. Doctors, lawyers, educators, accountants, engineers, and people in a wide variety of professions and businesses participate in professional development to learn and apply new knowledge and skills that will improve their performance on the job. In education, research has shown that teaching quality and school leadership are the most important factors in raising student achievement. For teachers and school and district leaders to be as effective as possible, they continually expand their knowledge and skills to implement the best educational practices. Educators learn to help students learn at the highest levels. Many people may not be aware of their local school system's methods for improving teaching and student learning. Professional development is the only strategy school systems have to strengthen educators' performance levels. Professional development is also the only way educators can learn so that they are able to better their performance and raise student achievement. Many misunderstandings exist about professional development, its purpose, and how it functions. This publication is an effort to answer basic questions and to inform and engage more people in strengthening the quality and improving the results of professional development.