How do I import modules or install extensions in PostgreSQL 9.1+?

Postgrseql 9.1 provides for a new command CREATE EXTENSION. You should use it to install modules.

Modules provided in 9.1 can be found here.. The include,

adminpack , auth_delay , auto_explain , btree_gin , btree_gist
, chkpass , citext , cube , dblink , dict_int
, dict_xsyn , dummy_seclabel , earthdistance , file_fdw , fuzzystrmatch
, hstore , intagg , intarray , isn , lo
, ltree , oid2name , pageinspect , passwordcheck , pg_archivecleanup
, pgbench , pg_buffercache , pgcrypto , pg_freespacemap , pgrowlocks
, pg_standby , pg_stat_statements , pgstattuple , pg_test_fsync , pg_trgm
, pg_upgrade , seg , sepgsql , spi , sslinfo , tablefunc
, test_parser , tsearch2 , unaccent , uuid-ossp , vacuumlo
, xml2

If for instance you wanted to install earthdistance, simply use this command:

CREATE EXTENSION earthdistance;

If you wanted to install an extension with a hyphen in its name, like uuid-ossp, you need to enclose the extension name in double quotes:

CREATE EXTENSION "uuid-ossp";

• Read more about contrib, and the modules available in 9.1.
• Read about the new extension infrastructure, and the SQL commands to manage it here You can now more easily uninstall a module, see DROP EXTENSION. You can also get an extension list, and there is basic support for version numbers.

While Evan Carrol's answer is correct, please note that you need to install the postgresql contrib package in order for the CREATE EXTENSION command to work.

In Ubuntu 12.04 it would go like this:

sudo apt-get install postgresql-contrib

Restart the postgresql server:

sudo /etc/init.d/postgresql restart

All available extension are in:

/usr/share/postgresql/9.1/extension/

Now you can run the CREATE EXTENSION command.