Consider a finite population of N items, where item i has a probability p to be defective, independent of the other units (in the generalized group testing allows different p_i). A group test is a binary test on an arbitrary group of items with two possible outcomes: all items are good, or at least one item is defective. The goal is to identify all items through group testing with the minimum expected number of tests. The optimum procedure, with respect to the expected total number of tests, is unknown even in the case where all pi are equal. In this talk, I shall review established results in the group testing literature and present new results characterizing the optimality of group testing procedures. In addition, I will discuss some open problems and conjectures. If time allows, then I will also discuss related problems of imperfect testing and the estimation of p based on grouped data.