The 4.2 Berkeley Software Distribution of UNIX for the VAX provided many new facilities. This paper highlights the changes to 4.2BSD that appear in 4.3BSD. The changes to the system have consisted of improvements to the performance of the existing facilities, as well as enhancements to the current facilities. Performance improvements in the kernel include cacheing of path name translations, reductions in clock handling and scheduling overhead, and improved throughput of the network. Performance improvements in the libraries and utilities include replacement of linear searches of system databases with indexed lookup, merging of most network services into a single daemon, and conversion of system utilities to use the more efficient facilities available in 4.2BSD. Enhancements in the kernel include the addition of subnets and gateways, increases in many kernel limits, cleanup of the signal and autoconfiguration implementations, and support for windows and system logging. Functional extensions in the libraries and utilities include the addition of an Internet name server, new system management tools, and extensions to dbx to work with Pascal. The paper concludes with a brief discussion of changes made to the system to enhance security.