A dynamic, equilibrium model of long term (implicit) labour contracts under incomplete but symmetric information is developed. Workers are assumed to be risk averse and of unknown ability or productivity. Risk neutral firms learn, as do workers, about each worker's productivity by observing the worker's output over time. It is shown that equilibrium contracts provide for wages which never decline with age and increase only when the worker's market value increases above his current wage. In addition to characterizing the equilibrium wage contract, we also derive some of its implications for the behaviour of aggregate wages across various groups of workers. These implications explain some findings in the recent empirical literature on age-earnings profiles. In particular our model can explain why earnings may be positively related to experience even after controlling for productivity, as some empirical studies have indicated.