This document is primarily concerned with the synchronisation of directory systems where the central publishing mechanism is based on X.500 with LDAP or DAP acess. It surveys the issues of synchronisation, but is not prescriptive in terms of procedure or products. Synchronisation can be viewed as the process of coordinating directory information that is held in multiple databases. This document is primarily concerned with synchronisation for the primary purpose of publication, in which there is a single (perhaps distributed, and possibly duplicated) publication mechanism, such as an LDAP-acessed X.500 system. This publication system may be distributed (e.g. as is the intent of an X.500 directory system), but may also be focussed on a single database.