Methods that allow the analysis of a single cell's genome or transcriptome are invaluable for characterizing the heterogeneity and plasticity within cell populations. A method to profile chromatin accessibility now joins the single-cell analysis toolbox. Buenrostro et al., who developed ATAC-seq (assay for transposon-accessible chromatin) for the rapid mapping of genome regulatory regions, adapt the technique using a commercial microfluidic device to allow chromatin accessibility profiling in single cells. The authors report that variation in the accessibility of regions bound by certain regulatory factors differs between cell types, and this information can be used to deconvolve cellular mixtures. Variations in single-genome accessibility also correlates with chromosome conformation, indicating that single-cell ATAC-seq can capture three-dimensional genome structure de novo.