Abstract: Background: The characterisation of testicular germ cell tumours (TCGTs) has to-date been limited to panel or whole-exome sequenced (WES) datasets. By using the full set of whole-genome sequenced (WGS) TCGTs from the Genomics England platform, we intend to fully characterise TCGTs, thereby contributing substantially to the knowledge underpinning effective genomic testing for this disease. This work will validate and facilitate the identification of genomic changes at the time of TGCT diagnosis, which may ultimately assist and influence effective clinical management. Methods: We increase the discovery power for novel SNV, indel, copy number, and structural variant drivers of TGCTs by using a set of ∼50 fresh-frozen, WGS tumours. After applying a rigorous quality control process to the provided variants, we use multiple tools separately and in combination to elucidate the various genomic aberrations present in TGCTs. This includes: copy number variants, structural variants, coding, noncoding, germline, and somatic drivers, the presence of selection, the variety of mutational signatures, the heterogeneity (subclonality) present, and the ordering of mutational events. In addition, we separate the sample set in multiple directions (seminomatous:nonseminomatous, primary:metastasis, early:late onset, etc) to explore clinical stratifiers. Results: Early analyses have identified novel mutational drivers, copy number aberrations, and structural variants. We are exploring the subclonality present, categorising drivers, copy number aberrations, and structural variants as predominantly clonal or subclonal, alongside timing these various aberrational events. Based on this, we will categorise TGCTs into genomic groups, which may prove useful forclinical management