Resources are one of the main reasons for using incremental processing. This chapter provides characterizations of resources and related terms. The most important point about resources in the context of cognitive processing is that the behavior of a cognitively adequate model is influenced by how much of each required resource is available. Because most resources are limited, cognitive systems cannot be perfectly, unboundedly rational, but they are rational within bounds. Herbert Simon's idea is mainly directed against the notion of a perfect, unbounded rationality, which was the prevalent theory in the 1940s and 1950s when he first proposed the idea. Simon showed that unbounded rationality is unsuited to explain the behavior of natural agents, because the computational and predictive ability of natural agents are too restricted. The frame problem was first observed by McCarthy and Hayes and leads to an explosion of complexity, which means it causes problems in systems that have to cope with limited resources.