I-O psychologists work to understand and influence how people behave in the workplace – the place where most adults in industrialized societies spend a significant part of their lives. This chapter will describe I-O psychology as a profession as well as its history. This chapter addresses the primary areas of research and practice in industrial and organizational (I-O) psychology; the contexts and organizations in which I-O psychologists work, as well as the training that I-O psychologists receive; the primary professional organizations to which I-O psychologists belong; the historical eras that have affected I-O psychology (e.g., World War I era, Civil Rights era) and various phases in the history of I-O psychology; the key legal and global issues surrounding I-O psychology; and current issues around I-O psychology.