Maslow's hierarchy of needs theory proposes that people are motivated to fulfill basic physiological needs before moving on to safety, social, esteem and self-actualization needs. Herzberg's two-factor theory distinguishes between motivators like achievement and responsibility that create job satisfaction, and hygiene factors like company policies that prevent dissatisfaction. Both theories have been widely studied but lack strong evidence and may oversimplify human motivation, which can vary between individuals and cultures. Overall, they recognize motivation as internal rather than dependent solely on external factors.