Equity theory, also known as justice theory, is an important concept in social psychology and organisational psychology. It was first developed by John Stacey Adams in the 1960s and deals with the perception of fairness and justice in social relationships, particularly in the context of work.

This theory postulates that people endeavour to achieve a balance between their own investments (e.g. work effort, commitment) and the resulting rewards (e.g. salary, recognition). If someone feels that their input and output are out of balance, this can lead to dissatisfaction. This imbalance is referred to as "cognitive dissonance".

To reduce this cognitive dissonance, individuals have various options. They can either increase their efforts to receive a fairer reward or they can change their perception of the situation to justify the unfairness. These adjustments can strongly influence a person's work behaviour and motivation.

It is important to note that equity theory is not only relevant at an individual level, but also at an organisational level. Organisations that provide fair pay and recognition tend to have happier and more motivated employees. This can have a positive impact on productivity and the working atmosphere.

Equity theory also has implications for leadership and management in organisations. Managers should ensure that their decisions and reward systems are perceived as fair in order to maintain the commitment and loyalty of their employees.

In summary, it can be said that equity theory makes an important contribution to explaining the behaviour of people in social and organisational contexts. It emphasises the importance of fairness and justice in shaping relationships and structures in the world of work.