The study is a multicenter, randomized, double-blind, placebo-controlled, active comparator, parallel-group study of 2 dose levels of lemborexant for approximately 6 weeks in approximately 950 participants, 55 years or older with insomnia disorder. Participants will be males 65 years or older or females 55 years or older. At least 60% of the participants will be age 65 years or older. The study will have 2 phases: The Prerandomization Phase and the Randomization Phase. Including both phases, the study will last for a minimum of 65 and a maximum of 81 days per participant.