Is personality genetically determined? If so, how can we ever change?

There is increasing evidence that many personality traits such as stress vulnerability, imaginativeness, cheerfulness, aggression, and shyness have a genetic component. However, genes do not act in a vacuum; the behaviors that people exhibit are also determined in part by their environment, and in part by their conscious will. For example, even the most genetically intelligent child will fail to thrive in an extremely deprived environment. And sometimes people decide to change. Techniques such as biofeedback and relaxation can help those very vulnerable to stress develop more adaptive responses to tension.

I've heard a lot of criticism of many of Freud's ideas about personality. Which, if any, are still regarded as useful today?

While Freud's theories have been roundly criticized for being untestable, scientifically unsupported, and sexist, there is much of value in his work. Concepts such as the unconscious, defense mechanisms, and the role of childhood experience on adult patterns of behavior have become fundamental assumptions underlying the way both psychologists and lay people think about personality. These ideas were all pioneered by Freud and continue to help us understand personality functioning and development.