Maslow's hierarchy of needs proposes that people are motivated to fulfill lower level needs like physiological and safety needs before pursuing higher level needs like esteem and self-actualization. Alderfer's ERG theory simplifies this by grouping needs into existence, relatedness, and growth. Herzberg identified motivators related to the job itself and hygiene factors about the environment. McClelland focused on power, affiliation, and achievement needs. McGregor proposed positive Theory Y and negative Theory X views of human motivation.