psychology, with research articles appearing in a number of academic journals, including those mentioned later in this article. One of the frequent challenges of HRM is dealing with the notion of unitarism (seeing a company as a cohesive whole, in which both employers and employees should work together for a common good) and securing a long-term partnership of employees and employers with common interests. Careers There are half a million HR practitioners in the United States and millions more worldwide. The Chief HR Officer or HR Director is the highest ranking HR executive in most companies. He or she typically reports directly to the chief executive officer and works with the Board of Directors on CEO succession. Within companies, HR positions generally fall into one of two categories: generalist and specialist. Generalists support employees directly with their questions, grievances, and work on a range of projects within the organization. They "may handle all aspects of human resources work, and thus require an extensive range of knowledge. The responsibilities of human resources generalists can vary widely, depending on their employer's needs." Specialists, conversely, work in a specific HR function. Some practitioners will spend an entire career as either a generalist or a specialist while others will obtain experiences from each and choose a path later. The position of HR manager has been chosen as one of the best jobs in the US, with a #4 ranking by CNN Money in 2006 and a #20 ranking by the same organization in 2009, due to its pay, personal satisfaction, job security, future growth, and benefit to society. Human resource consulting is a related career path where individuals may work as advisers to companies and complete tasks outsourced from companies. In 2007, there were 950 HR consultancies globally, constituting a US$18.4 billion market. The top five revenue generating firms were Mercer, Ernst & Young, Deloitte, Watson Wyatt (now part of Towers Watson), Aon (now merged with Hewitt), and PwC consulting. For 2010, HR consulting was ranked the #43 best job in America by CNN Money. Some individuals with PhDs in HR and related fields, such as industrial and organizational psychology and management, are professors who teach HR principles at colleges and universities. They are most often found in Colleges of Business in departments of HR or Management. Many professors conduct research on topics that fall within the HR domain, such as financial compensation, recruitment,