Historically, the most important results in argument structure have come from those studying the properties of the Lexicon as a module of grammar. The second section of this chapter gives the perspective on the issues from the vantage point of the Lexicon, i.e. the practical problem of deciding how much and what kind of information is necessary for the listing of verbal lexical entries. The third section gives a morphosyntactic overview of the patterns in argument structure related to Subject selection. The chapter reviews the correlations with one other important interacting syntactic phenomenon, namely case. The relationship between argument structure and the architectural interfaces are explored. The chapter discusses the interaction with discourse and cognitive facts, and the modular interaction between the Lexicon and the syntactic computation. The chapter ends with a plea for linguists to revisit the serious and still unresolved problem of 'selection'.