Internet Library

These are free books that are available on the Internet that relate to the X.400 and X.500 standards. The books are in either PDF or HTML format, and some require you to register before you can access them.

X.400 (1999)	X.411 (1999)	X.413 (1999)	X.420 (1999)
International Telecommunication Union	International Telecommunication Union	International Telecommunication Union	International Telecommunication Union
Freely available	Freely available	Freely available	Freely available
X.500 (2005)	X.509 (2005)	X.511 (2005)	X.525 (2005)
International Telecommunication Union	International Telecommunication Union	International Telecommunication Union	International Telecommunication Union
Freely available	Freely available	Freely available	Freely available
ASN.1 - Communication Between Heterogenous Systems	ASN.1 Complete	Open Systems Networking OSI and TCP/IP	Understanding OSI
Olivier Dubiosson	John Larmouth	David M. Piscitello A. Lyman Chaplin	John Larmouth
Registration required	Registration required	Freely available	Freely available
LDAP - Design and Implementation	Understanding X.500 - The Directory
Steven Tuttle Ami Ehlenberger Ramakrishna Gorthi Jay Leiserson Richard Macbeth Nathan Owen Sunil Ranahandola Michael Storrs Chunhui Yang	David Chadwick
Freely available	Freely available
OSI Asbtract Data Manipulation API (XOM), Issue 3	API to Directory Services (XDS), Issue 3	API to Electronic Mail (X.400), Issue 3
The Open Group	The Open Group	The Open Group
Registration required	Registration required	Registration required