Grammatical encoding refers to the processes involved in organizing a non-linguistic message into an ordered set of representations that can then be phonologically formulated and eventually be articulated. This includes the selection and retrieval of syntactic and lexical representations, as well as determining the appropriate morphological forms and constituent order for a given message. This chapter first describes a consensus view of the architecture of grammatical encoding and what we know about its underlying cognitive/neural mechanisms. It then discusses a number of topics that are under debate or not yet well understood. These include questions about the stages of processing, the nature of grammatical representations, the degree of incrementality and advance planning, and the degree of modularity/interactivity (among others). Despite these many open questions, we have made significant progress in our understanding of grammatical encoding and the chapter ends by highlighting important insights we have gained so far.