The structure of Philip Sidney's Astrophil and Stella is governed by a distinctive and complex set of proportions, found also in the sonnet sequences of Fulke Greville and Robert Sidney written under its influence. For all these works to be ordered around the same set of proportions indicates a remarkable degree of careful planning and precise execution, and in turn affects their meaning. The tremendous effort of constructing the sequences according to intricate mathematical patterns suggests that the patterns themselves held a particular significance, one that requires investigation for the light it throws on these authors' intentions in composition. In this study Tom Parker reveals cosmological ideas implicit in the form of Astrophil and Stella, ideas which not only undermine much of the romantic and biographically-based criticism of the sequence, but call into question how we should read the sonnet sequences that were influenced by Sidney, both within and beyond his immediate circle. As well as those of Greville and Robert Sidney, the book looks in detail at the sonnet sequences of Giordano Bruno, Mary Wroth, Henry Constable, Barnabe Barnes, and Michael Drayton, to determine the extent to which the sonnet vogue of the 1590s incorporated Sidney's broader cosmological concerns.