Chronic rhinosinusitis (CRS) is a globally prevalent inflammatory disease that seriously impairs quality of life. While advances in monoclonal antibody (mAb) therapies have transformed CRS management, mAbs have failed to induce disease remission with symptom return upon withdrawal of treatment. This pattern suggests that, in addition to inflammatory pathways, alternative mechanisms may contribute to CRS pathogenesis. In 2025, our department published the first benchmarking study for sinus microbiome sequencing, finding that the 16S rRNA methods applied in all prior studies significantly distorted samples, with only metagenomic analysis providing accurate results. Hence, to definitively investigate the role of dysbiosis in CRS, we have conducted the first international sinus microbiome study to integrate paired shotgun metagenomic and 16S rRNA sequencing. Samples were collected by endoscopically guided middle meatal swab from 432 participants (174 controls; 155 CRS with nasal polyps [CRSwNP]; 103 CRS without nasal polyps [CRSsNP]), across 14 centres in 9 countries. Metagenomic libraries were prepared using the ONT native barcoding kit and sequenced on the PromethION platform. Data was analysed using an in-house pipeline and custom database with Sourmash for taxonomic assignment. CRS microbiomes differed significantly from non-CRS controls and between disease phenotypes. Corynebacterium accolens was most strongly associated with health (p=0.001, β=5), followed by D. pigrum (p=0.017, β=2). In contrast, P. aeruginosa, S. pneumoniae, and H. influenzae were significantly enriched in CRS (p<0.05, ß=3;4;4). Staphylococcus aureus was associated with CRSwNP (p=0.033, ß=6), while C. kefirresidentii was selectively enriched in CRSsNP (p=0.008, ß=4). This study provides the first international evidence defining dysbiosis in CRS and linking clinically relevant bacteria to both disease presence and phenotype. These findings recentre the sinonasal microbiome in CRS aetiopathogenesis and support its potential as a source of diagnostic, prognostic, and therapeutic targets.