Book entry is a system of tracking ownership of securities where no certificate is given to investors.
Also, replacement costs for certificates are high in case one loses them, while book-entry ownership can never be lost thanks to technological backups.
On August 8, 2006, the SEC approved a rule changed by NASDAQ, NYSE and AMEX requiring all listed securities (except certain debt securities) to be eligible for a direct registration system ("DRS") as of March 31, 2008.
DRS is an entirely electronic book-entry style system that does not involve physical stock certificates.
The rule change does not eliminate physical certificates, but requires issuers to be eligible for entirely electronic recording of securities ownership.