In this course we are going to study an important tool to analyze collected data: clustering. Clustering is the process of dividing data into useful or sensible groups. A sensible division should resemble the data's natural structure. Sometimes the goal is that each cluster should contain as many items of a similar kind as possible ( for example in data compression). Clustering is a very natural way to analyze and structure data. Especially in natural sciences we are working with data whose structure is unknown to us. An example is the human DNA, that humankind is trying to decode. Clustering can be a very powerful tool in such cases.