Women are sometimes labeled as nags, whereas men are labeled as wife beaters. This paper explores the different expressions of aggression by men and women. It presents different viewpoints, opinions, and studies by different sociologists and psychologists regarding gender differences in aggression.“Aggression is an intentional behavior that is done to cause harm or pain to another person” (Encyclopedia of Psychology, 2008). The important point in this definition of aggression is the intent to cause harm to another person. Harm caused to another human being through accidents is not considered as aggression. Aggression can either be physical or verbal, and it may be successful or unsuccessful (Spaulding, 2008). Nevertheless, whatever form aggression may take, it is always important to note that aggression may be caused by various factors and reasons. Biologists will claim biological reasons for gender differences in aggression. sociologists will credit socio-cultural factors, and some psychologists will lay claim to both socio-cultural and biological reasons for gender differences in aggression. These points shall be discussed in this paper.Aggression is often attributed to biological factors. These biological factors mostly have something to do with the body’s hormones. Testosterone in adult males is “about ten times as high as those in adult females” (Goldberg, 1993, as quoted by Sanderson, 2001). This hormone is largely credited for aggression, dominance, and competitive behavior in men. Many biologists and practitioners believe that men are naturally prone to more aggressive behavior because of this hormone. In the process, they are also more prone to physical outbursts of anger and aggression as compared to their female counterparts. Research studying levels of testosterone in prison inmates revealed that those convicted of violent crimes hadhigher levels of testosterone than those convicted of non-violent offenses.