Closely spaced transcription signals formally assigned to different, neighboring genes can functionally interact both in their authentic genomic context as well as in engineered transgene constellations. To describe these promoter crosstalk effects quantitatively and qualitatively, we used various combinations of inducible and constitutive expression signals linked in cis. Our results demonstrate that such interactions can be bidirectional, making it difficult to unambiguously assign a particular promoter element exclusively to a specific gene. We show that especially for inducible promoters, crosstalk effects can cause a substantial distortion in the expression of proximal genes, challenging established strategies in generating transgenic animal models and tissue culture systems. Furthermore, these findings provide guidelines for the design of transgenic transcription units that, while refractory to interactions with their chromosomal environment, leave the expression programs of neighboring genes largely untouched.