How to use yum to list installed packages

yum list package_name

For example:

[root@myserver ~]# yum list compat-libcap1
Loaded plugins: product-id, rhnplugin, search-disabled-repos, security
This system is receiving updates from RHN Classic or RHN Satellite.
Installed Packages
compat-libcap1.x86_64                                                   1.10-1                                                   @test-rhel-x86_64-server-6
Available Packages
compat-libcap1.i686                                                     1.10-1    

See also "yum command cheat sheet" from RH for a good overview.