It is needed to organize the data in different groups for various purposes, where clustering is useful. The chapter covers Data Clustering in the detail, which includes; introduction to data clustering with figures, data clustering process, basic classification of clustering and applications of clustering, describing hard partition clustering and fuzzy clustering. Some most commonly used clustering method are explained in the chapter with their features, advantages, and disadvantages. A various variant of K-Means and extension method of hierarchical clustering method, density-based clustering method and grid-based clustering method are covered.