 Our genome is a lot like a book. When cells need information critical to their function, they must physically crack the genome open to arrive at the right chapter or gene sequence. Often, the relevance of details from Chapter 1 isn't clear until Chapter 10. Similarly, non-coding sequences often control the expression of genes far away in linear genomic distance but relatively close in three-dimensional space. Now, a new method of probing these regions could help scientists gain more information from much less starting material and, in the process, help us learn more about the book of life. The technique is called HICAR, short for HIC on Accessible Regulatory DNA. HICAR builds off the HIC method, which uses high throughput sequencing to detect how different regions of genomic DNA interact with each other. Specifically, HICAR targets the regions of chromatin that are open and accessible to proteins with information about gene regulation. In HICAR, cells are first cross-linked to fix the spatial interaction of the genome. They're then treated with a tagmentation complex that utilizes the enzyme TN5 transposase to insert an engineered DNA adapter into the accessible region of the DNA. After tagmentation, a restriction enzyme digests the DNA into shorter fragments, followed by proximity ligation, to ligate the TN5 adapters to their nearby genomic DNA. Next, the cross-links are reversed. The purified DNA is linearized by digestion with a second restriction enzyme and then circularized by intramolecular ligation. PCR amplification then generates HICAR libraries for next-generation sequencing, with digested genomic DNA reads labeled R1 and open chromatin reads labeled R2. In proof-of-principle experiments, HICAR outperformed several existing methods for simultaneously capturing regulatory chromatin sequences and 3D genome structure. The R2 reads of a HICAR library for human embryonic stem cells and immune cells overlapped well with reads gathered by attack-seq and chip-seq, the gold standards for analyzing chromatin regulatory sequences. And despite using only less than 10% of the sequencing depth of conventional HICI, the gold standard for 3D genome analysis, HICAR generated a chromatin contact matrix similar to that of HICI at different resolutions. Compared with the track-looping technique for detecting long-range chromatin interactions, HICAR required 1,000 times fewer input cells, yielded more complex libraries, and identified about 18 times more long-range paired-end tags which are useful for 3D analysis across long genomic distances. In addition to being simpler and more cost-effective than existing methods, HICAR also detects the presence of so-called poised gene promoters, which do not immediately drive gene expression. Interestingly, these poised promoters can function as silencer-like elements over long genomic distances to repress distal genes through long-range chromatin looping between promoters. Notably, HICAR yields high-quality and reproducible open chromatin and 3D genome maps, in some cases with as few as 30,000 cells purified from precious clinical samples. Overall, findings suggest that the HICAR method is a robust, sensitive, and cost-effective assay for examining how chromatin is organized in cell nuclei, making it broadly applicable for multi-omics analysis of low-input tissue and cells.