Motivation is the psychological process that guides and directs an individual toward the achievement of particular goals (Buford, Bedeian, & Lindner, 1995): an internal drive to realize unfulfilled desires (Higgins , 1994). In other words, motivation is the internal vigor to acquire desired needs and achieve personal or organizational goals. According to Smith (1994), motivation is an important factor for a company's survival in today's dynamic society as highly motivated employees are more productive. Therefore, the question of how to improve motivation is a complex issue that management should consider. Employee motivation is influenced by several factors, such as their needs, work environment and target performance. If managers want to improve employee motivation, they should understand employee motivation in different aspects. There are four main theories: Abraham Maslow's Hierarchy of Needs, Frederick Herzberg's Two-Factor Theory, Victor Vroom's Expectancy Theory, and John Stacey Adams' Equity Theory. Maslow and Herzberg's theories focus on satisfying people's needs to increase their motivation, known as content theories. However, Vroom and Adams' theories recognize the complexity of motivation, which is a process theory, assume that employees are motivated by their own performance. This essay will compare the similarities and differences between these four theories and articulate how management can critically use these theories to motivate employees. Employee motivation is optimal when external factors are tailored to individuals' needs. According to Maslow's hierarchy of needs (1954), people's needs are divided into physiological, safety, relationship, esteem and self-accomplishment... in the center of the card... and the results will influence people's motivation , in other simple words, if the expectation has been met, motivation will increase. Employee fairness is also linked to the comparison between one's own rewards and those of others. People feel that their rewards are equal to those of the reference people, so they subjectively feel fair, which will lead to greater motivation. Since the advantages and disadvantages of the four theories are obvious, needs theory does not build the right relationship between satisfaction and motivation, expectancy and equity theories refer to the need for reward to satisfy individuals' needs, which is linked to Maslow and Herzberg's theory of needs. Therefore, management should critically use these four theories, considering employee needs, tying rewards to performance, and properly accessing equity among employees, thus comprehensively understanding employee motivation..