This paper is concerned with such concepts as topic, focus and cognitive status of discourse referents, which have been included under the label information structure (alternatively information status), as they are related in some sense to the distribution of given and new information. It addresses the question of which information structural properties are best accounted for by grammatical constraints and which can be attributed to non-linguistic constraints on the way information is processed and communicated. Two logically independent senses of given-new information are distinguished, one referential and the other relational. I discuss some examples of linguistic phenomena that pertain to each of these different senses and show that both are linguistically relevant and must be represented in the grammar. I also argue that phenomena related to both senses have pragmatic effects that do not have to be represented in the grammar since they result from interaction of the language system with general pragmatic principles that constrain inferential processes involved in language production and understanding.