Primary insomnia (PI) is an increasing concern in modern society. Cognitive-behavioral therapy for insomnia is the first-line recommendation, yet limited availability and cost impede its widespread use. While hypnotics are frequently used, balancing their benefits against the risk of adverse events poses challenges. This review summarizes the clinical and preclinical evidence of acupuncture as a treatment for PI, discussing its potential mechanisms and role in reliving insomnia. Clinical trials show that acupuncture improves subjective sleep quality, fatigue, cognitive impairments, and emotional symptoms with minimal adverse events. It also positively impacts objective sleep processes, including prolonging total sleep time, improving sleep efficiency, reducing sleep onset latency and wake after sleep onset, and enhancing sleep architecture/structure, including increasing N3% and REM%, and decreasing N1%. However, methodological shortcomings in some trials diminish the overall quality of evidence. Animal studies suggest that acupuncture restores circadian rhythms in sleep-deprived rodents and improves their performance in behavioral tests, possibly mediated by various clinical variables and pathways. These may involve neurotransmitters, brain-derived neurotrophic factors, inflammatory cytokines, the hypothalamic-pituitary-adrenal axis, gut microbiota, and other cellular events. While the existing findings support acupuncture as a promising therapeutic strategy for PI, additional high-quality trials are required to validate its benefits.