The FLSA requires that covered, nonexempt employees be paid at least the federal minimum wage of $7.25 per hour for all hours worked, plus time and one-half their regular hourly rates for hours worked beyond 40 per week.
With few exceptions, to be exempt an employee must (a) be paid at least $23,600 per year ($455 per week), and (b) be paid on a salary basis, and also (c) perform exempt job duties. These requirements are outlined in the FLSA Regulations (promulgated by the U.S. Department of Labor). Most employees must meet all three "tests" to be exempt.
An employee who meets the salary level tests and also the salary basis tests is exempt only if s/he also performs exempt job duties. These FLSA exemptions are limited to employees who perform relatively high-level work. Whether the duties of a particular job qualify as exempt depends on what they are. Job titles or position descriptions are of limited usefulness in this determination. (A secretary is still a secretary even if s/he is called an "administrative assistant," and the chief executive officer is still the CEO even if s/he is called a janitor.) It is the actual job tasks that must be evaluated, along with how the particular job tasks "fit" into the employer's overall operations.
http://www.flsa.com/coverage.html
Generally managers, engineers, and most salaried office jobs are "exempt". Lately more focus has gone towards defining who exactly is an exempt vs non-exempt salaried employee in white collar office jobs.