Dunedin City Libraries mobile and home services team leader Jo Bailey said the volunteers were delivering books and other resources to about 200 people who found it hard to visit the libraries.
It is likely that at least an estimated 600,000 books and other resources have been delivered to city homes over the past 20 years.
She acknowledged that the overall total might have reached about a million items since the home delivery tradition began, about 1938.
Over the years, people receiving the books had ranged in age from about 14 to at least 100, after physical or mental health difficulties made it hard for them to visit the libraries themselves.
The volunteers were doing ''invaluable'' work, because although librarians selected the books to match individual tastes, they lacked the resources to make the deliveries themselves.
The books and the increasingly popular talking books are delivered by the volunteers in red bags to the same readers, once a month.
Romance and ''cosy'' mysteries-''not too brutal''- were popular, although some readers were also keen on biography and physics.
She found it ''fulfilling to be able to help out'' as part of the home delivery arrangements. The service boosted ''community wellbeing'', providing a valuable ''connection with people''.
Bob McRae still provides books for two families in St Kilda, where he once lived.
''It's a connection with the people who lived there, and it's a good chance to catch up.
''They're such nice people,'' Mr McRae said.
