Find out version of libraries installed in Linux

It is just one of those things about Gentoo that I never could remember. I was needing to find out what version of libgtk I was using, and for the life of me, I couldn't remember what command was required to find it out, until someone kindly told me that you can do that using 'emerge -pv'.

Funnily, it didn't come to me intinctively, even though I use the command to query before upgrading packages all the time. It is just that I've never thought to use it as a tool for library version checking. Guess that might be the same way on other distributions to find out about their the versions of their installed libaries as well. For .deb (Debian/Ubuntu) based distros, try the 'apt' command, while those on the .rpm (RedHat/SuSE) based distros, try 'rpm' or 'yum'.

What package names should you search under? Frankly, I don't have a clue. If there is one bad thing about having a fragmented market distribution base like Linux, it'll have to be the confusion of configuration layouts among the competing distributions, which makes finding a solution a rather time consuming process.