The PostgreSQL Global Development Group &legal; The first part of this manual is the description of the client-side programming interfaces and support libraries for various languages. The second part explains the PostgreSQL approach to extensibility and describe how users can extend PostgreSQL by adding user-defined types, operators, aggregates, and both query language and programming language functions. After a discussion of the PostgreSQL rule system, we discuss the trigger and SPI interfaces. The third part documents the procedural languages available in the PostgreSQL distribution. Proficiency with Unix and C programming is assumed. &libpq; &lobj; &libpqpp; &libpgtcl; &libpgeasy; &ecpg; &odbc; &jdbc; &pygresql; &lisp; &arch-pg; &extend; &xfunc; &xtypes; &xoper; &xaggr; &rules; &xindex; &indexcost; &gist; &trigger; &spi; &xplang; &plsql; &pltcl; &plperl;