Insects live in a highly complex odorant world. Within a variety of odor blends, they need to locate potential food sources, mates, and oviposition sites to gain reproductive success. In nature, volatile cues leading to a resource are always present with numerous other volatiles—here referred to as background odor—which may affect the parasitoid's response to resource-indicating cues. Three different types of background odor are discussed in this article: (a) irrelevant background odor, (b) background odor that may mask the resource-indicating signals, and (c) background odorants that may “sharpen the view” for resource-indicating odor and enhance the response to these. Odor orientation to resources especially in herbivorous and parasitic insects are addressed.