Vegetation classification is a useful tool for basic and applied research as well as for environmental management. As classification of vegetation serves many different purposes, there is no single approach to defining vegetation types. Establishing formalized standard procedures is desirable, however, because the purposes and uses of vegetation classifications are similar in different countries and regions. With the aim of promoting methodological standardization in classification across countries and vegetation scientists, this manuscript is centered on two ideas: (1) the need to explicitly distinguish between the conceptual activities involved in the definition of vegetation types (membership determination, characterization, validation and naming); and (2) the need to perform assignments of new vegetation observations to previously defined vegetation types in accordance with how these types were originally defined, a concept that we refer to as consistency in assignment. We demonstrate that our conceptual framework provides a useful tool to better understand what classification methods do. In order to manage and use classifications in a better way, vegetation scientists should produce, store and report the rules that provide consistent assignments to vegetation types.