Pain and sleep are closely linked physiological processes that support overall health and functioning. Increasing evidence shows a dynamic, bidirectional relationship: poor sleep increases pain sensitivity, while chronic pain disrupts normal sleep. Both conditions are highly prevalent and significantly impair quality of life, making them major public health concerns. Chronic pain, defined as pain lasting more than three months, affects around 17% of adults in Spain. Insomnia, though common, is harder to define due to its overlap with medical and psychiatric conditions. It may present as a symptom, a syndrome, or a formal sleep disorder, leading to variability in prevalence estimates. Current diagnostic criteria, including DSM-5 and the International Classification of Sleep Disorders, Third Edition (ICSD-3), adopt the unified concept of chronic insomnia disorder, defined as persistent difficulty with sleep initiation, maintenance, or quality, despite adequate opportunity for sleep, and associated with daytime impairment. ICSD-3 distinguishes three types of insomnia: * Chronic insomnia disorder: symptoms ≥3 times/week for ≥3 months; * Short-term insomnia disorder: symptoms lasting less than 3 months; * Other insomnia disorder: symptoms not meeting criteria for the above. About one-third of the general population reports insomnia symptoms. However, when both night symptoms and daytime impact are considered, the prevalence of chronic insomnia disorder is estimated at 6-10%. Women are more frequently affected, with a female-to-male ratio of about 1.4:1. Despite this, few studies have assessed insomnia specifically in people with chronic non-cancer pain. This gap is important, as untreated insomnia may worsen pain and reduce treatment efficacy, reinforcing a vicious cycle. This observational study (PainSomnia) aims to estimate the prevalence of chronic insomnia among adults with chronic non-cancer pain. The results will help support integrated, individualized treatment approaches that address both sleep and pain in this high-risk population.