It is a simple question, but difficult to answer: how are concepts organized and represented in our brain? Many scientists ? in linguistics semanticists, psycholinguists and neurolinguists ? tried to answer this question and so I have described some of the semantic and psychological hypothesis and theories in part 1 of the diploma thesis. These theories are the Structuralism, Conceptual Semantics, the theory of Distinctive Features, the theory of Universal Primitives/ Semantic Primes, the Prototype theory, the Connectionism, the Embodiment-hypothesis, the Sensory/Functional-theory, the Organized Unitary Content-hypothesis and the Domain-Specific theory.Part 2 delineates some studies, relevant for the questions of associations and prototypicality. Also, my own study (held in 2009/2010 in Graz, Austria) is being described and discussed. It focuses on typicality shown by associations and ratings, shown at five different semantic categories. The study is then compared with other similar German and English studies; it matches best with a German study carried out in Austria, suggesting that geographical factors are highly influencing typicality.The third and last part of the thesis gives an overview over the findings and discusses in detail the following topics: ?Prototypes?, ?Categories?, ?Categorization?, and the ?Representation and Organization of Concepts?. It comes to the conclusion that linguists, psychologists, neurologists and other scientists working on this topic have each their own theories. So there is need of a theory, which is based on interdisciplinary discussion and exchange of information.