Historical periods help organize music in relation to long-term processes, from changes in community life to shifts in institutions, technologies, and record markets. Dates are useful approximations rather than absolute musical boundaries: older repertories may remain active while new performance forms emerge. This section supports browsing by period and comparison of the conditions under which works were created, recorded, and circulated. It is important to distinguish the period a composition evokes from the moment it was performed or recorded, especially in reissues and retrospective documents.