The current chapter builds foundation for search arrays and hash functions. It also covers searching on sorted and un-sorted arrays. The approach utilizes vector sorting for search operations using key-value pairs. The chapter also introduces approaches such as self-organizing lists which do not utilize key values for searching rather uses expected frequency of accessing the key values for comparison purposes. The chapter also introduces hashing concepts and covers various approaches for hashing, such as hash functions, open hashing, and closed hashing. Analysis on the computation required with the deletion operation is also covered in the final part of chapter. The next chapter will introduce tree based indexing data structures such as 2-3 trees, B-tree and B+ tree.