Modification is a combinatorial semantic operation between a modifier and a modifiee. Take, for example, vegetarian soup: the attributive adjective vegetarian modifies the nominal modifiee soup and thus constrains the range of potential referents of the complex expression to soups that are vegetarian. Similarly, in Ben is preparing a soup in the camper, the adverbial in the camper modifies the preparation by locating it. Notably, modifiers can have fairly drastic effects; in fake stove, the attribute fake induces that the complex expression singles out objects that seem to be stoves, but are not. Intuitively, modifiers contribute additional information that is not explicitly called for by the target the modifier relates to. Speaking in terms of logic, this roughly says that modification is an endotypical operation; that is, it does not change the arity, or logical type, of the modified target constituent. Speaking in terms of syntax, this predicts that modifiers are typically adjuncts and thus do not change the syntactic distribution of their respective target; therefore, modifiers can be easily iterated (see, for instance, spicy vegetarian soup or Ben prepared a soup in the camper yesterday). This initial characterization sets modification apart from other combinatorial operations such as argument satisfaction and quantification: combining a soup with prepare satisfies an argument slot of the verbal head and thus reduces its arity (see, for instance, *prepare a soup a quiche). Quantification as, for example, in the combination of the quantifier every with the noun soup, maps a nominal property onto a quantifying expression with a different distribution (see, for instance, *a every soup). Their comparatively loose connection to their hosts renders modifiers a flexible, though certainly not random, means within combinatorial meaning constitution. The foundational question is how to work their being endotypical into a full-fledged compositional analysis. On the one hand, modifiers can be considered endotypical functors by virtue of their lexical endowment; for instance, vegetarian would be born a higher-ordered function from predicates to predicates. On the other hand, modification can be considered a rule-based operation; for instance, vegetarian would denote a simple predicate from entities to truth-values that receives its modifying endotypical function only by virtue of a separate modification rule. In order to assess this and related controversies empirically, research on modification pays particular attention to interface questions such as the following: how do structural conditions and the modifying function conspire in establishing complex interpretations? What roles do ontological information and fine-grained conceptual knowledge play in the course of concept combination?