Plants sense and respond to endogenous signals and environmental cues to ensure optimal growth and development. Plant cells must integrate the myriad transduction events into a comprehensive network of signalling pathways and responses. The phytohormone auxin occupies a central place within this transduction network, frequently acting in conjunction with other signals, to co-ordinately regulate cellular processes such as division, elongation and differentiation. As a non-cell autonomous signal, auxin also interacts with other signalling pathways to regulate inter-cellular developmental processes. As part of this especially themed edition of Plant Molecular Biology, we will review examples of 'cross-talk' between auxin and other signalling pathways. Given the current state of knowledge, we have deliberately focused our efforts reviewing auxin interactions with other phytohormone and light signalling pathways. We conclude by discussing how new genomic approaches and the Arabidopsis genome sequence are likely to impact this area of research in the future.