Clustering can be considered the most important unsupervised learning problem. In briefly, the process of organizing objects into groups whose members are similar in some way. This book presents an overview of existing clustering algorithms with a goal of providing useful advice and references to fundamental concepts accessible to the broad community of clustering practitioners.Determining the number of cluster is a running burning question for clustering. I tried to propose a method for clustering validation. I present taxonomy of clustering techniques, and identify crosscutting themes and recent advances. I also describe a big famous field of application of clustering- Image segmentation.