Aggressive behavior is a growing phenomenon in today's world. Many authors who dealt with and still deal with the concept of aggressiveness agree that aggressiveness represents harming a person. Aggressive behavior is a natural phenomenon that occurs in every human being. In this paper, we will talk about aggressiveness in general, its origin, patterns, and the resolution of conflicts that occur in kindergarten. Aggressiveness is not a one-size-fits-all concept, but branches into different types. Accordingly, there are open and covert forms of aggressiveness, reactive and proactive aggressiveness, relational, instrumental and hostile aggressiveness, verbal and physical, social and normal and abnormal aggressiveness. The patterns of the emergence of aggressiveness are different, but they are mostly divided into biological, social and psychological factors. As is already known, all children can be aggressive regardless of age and gender. However, mostly boys are the ones who are more aggressive and they usually use physical aggression, while girls use more verbal aggression. Aggression in kindergarten is a very common phenomenon. Most often, children react aggressively around some toy they want by fighting, pulling their hair, biting and so on. Conflicts between children are a very common occurrence in kindergarten. On the one hand, they can be positive because they help children solve problems, and on the other hand, they can be negative because they can lead to aggression. Types of conflicts are divided according to causes, participants and consequences. Conflicts can be resolved in different ways, non-violently and constructively, through negotiation, mediation, arbitration and the like. It is also very important to spot conflicts in time and prevent them properly.