In this chapter we will first present some reflections on theoretical issues related to classification in archaeology, one of the most important concepts for our good practice but that is still very little explored and very poorly understood by many of us. We will present some issues that are pertinent to the theory (and even metaphysics) of classification in general terms and given that the discussion about classification in biology has been more developed in comparison to archaeology, we will present a general scenario on how this has been explored in that discipline, in order to avoid having to “reinvent the wheel” in archaeology. The last part of the chapter will be dedicated to present how archaeology has been dealing with classification. We believe that terminology problems that should have been resolved more than 70 years ago still cause confusion, both among seasoned scholars and students, and they hamper the advancement of one of the pillars of the discipline, which is classification. The objective of this chapter is not to provide a general overview of the literature nor a history of archaeological classification, but mainly to point out recurring theoretical problems, which have been accumulating since the mid-20th century, and which in general are not being adequately addressed by contemporary approaches. We also aim to discuss some methodological aspects, presenting examples and possibilities of application of some classificatory schemes in archaeology. Although we tried to avoid an exclusively theoretical approach, we tend to focus on discussions from cultural evolutionary archaeology, and in general we defend and justify the use of a metaphysical pluralist approach using arbitrary kinds applied to the archaeological record.