Chapter 3 explores verbal group system and structure. In doing so for English and Spanish, it concentrates on what in SFL is referred to as univariate structure. Univariate structures are structures involving a single variable, which is repeated over and over again; they thus function as the realisation of recursive systems. The unit complexes introduced above (clause complexes, group complexes, word complexes and morpheme complexes) are structures of this kind. And some languages develop more delicate clause and group systems organised along these lines. The recursive tense systems in English and Spanish which we describe in this chapter are good examples. Chinese verbal groups on the other hand do not involve recursive systems realised by iterating structures and so have to be approached from a multivariate perspective.