Barry Cummins is a well-known journalist and reporter and the author of Missing: The Unsolved Cases of Ireland's Vanished Women and Children.
An updated version of the book, first published 15 years ago, is out now.
While none of the cases in question have been solved, there have been some developments which are detailed in the latest edition.
Barry joined us to discuss the difficulties faced by the families of missing people, and how investigations have changed over the years.
He spoke about the dynamic between families and journalists: "It's an uneven relationship in that families are desperate and they need media to publicise cases."
"We're all entitled to our privacy except for missing people. In order to publicise cases we find ourselves asking personal questions and looking for personal information."
Barry thinks things such as forensics, mobile phone technology and CCTV have made it easier than ever to find people.
"We stand a better chance now of being found. We leave more of a trace wherever we go, which didn't exist in the '90s, and also Gardaí treat missing persons cases with more seriousness now."
"I think it's time to revisit those older cases and see if any new policing methods can be brought to bear."
Listen to the interview in full by pressing the play button on this page.
