Dictionaries are data structures that support search, insert, and delete operations. One of the most effective representations is a hash table. Typically, a simple function is applied to the key to determine its place in the dictionary. Also presented are binary trees and red-black trees. Both tree methods use a technique similar to the binary search algorithm to minimize the number of comparisons during search and update operations on the dictionary. Finally, skip lists illustrate a simple approach that utilizes random numbers to construct a dictionary.