The expression of critical developmental genes can be regulated by multiple cis-regulatory modules (CRMs), and it has been suggested that remote CRMs are redundant to promoter proximal CRMs. But what is the function of these multiple CRMs and are they truly redundant? To answer this question, Angelike Stathopoulos and co-workers (p. 4075) examine two CRMs from the Drosophila snail gene locus and show that these CRMs interact in a non-additive manner to regulate snail expression. The researchers demonstrate that the CRMs drive distinct patterns of gene expression in early embryos. Furthermore, they report, the distal CRM acts to limit the expanded expression domain of the proximal CRM, whereas the proximal CRM serves to `dampen' the levels of expression driven by the distal CRM. Importantly, the CRMs are not functionally equivalent; only the distal CRM is required in snail transgenes to rescue snail mutants. Thus, the authors propose, complex interactions between CRMs are required for fine-tuning the patterns and levels of snail expression during development.