Conduct disorder embraces a wide spectrum of anti-social behaviours, only a proportion of which is necessary for diagnosis. This chapter covers some topics which have not received much attention with respect to aggressive children, yet may be important for understanding this symptomatic and etiological heterogeneity. Aggressive behaviour is phenomenologically diverse, and can be divided into a number of categories. Aggressive behaviour is a common characteristic of conduct disorder, and appears not only as straight aggression, but also as disruptive behaviour, annoying others and cruelty, and may be responsible for the dislike of conduct-disordered children often shown by other children. A motivational approach applied to the particular symptom of aggressiveness demonstrates the dangers of a simplistic approach to etiology, but beyond that has only limited usefulness. A cognitive approach is more likely to be relevant to the wide range of symptoms that normal individuals show.