Infertility, defined as the inability to achieve pregnancy within 12 months of regular unprotected sexual intercourse, affects one in six couples across the globe. A range of environmental and genetic factors may drive infertility, including the age-related decline of sperm and oocyte quality and quantity, infectious diseases, and rare Mendelian disorders such as cystic fibrosis. However, the exact cause remains undetermined in up to 28% of couples and 40% of women with infertility. Given that current treatments such as in vitro fertilisation pose physical, emotional, and financial burdens on couples and healthcare systems, a richer understanding of the biology and pathophysiology of infertility is urgently necessary. This project will conduct a genome-wide association study (GWAS) in ALSPAC and other participating cohorts. In addition, the project will conduct a GWAS of infertility (not in ALSPAC).