The topic of my talk at WordCamp Fraser Valley 2009 was Growing Up With Child Themes.  Briefly, a child theme is one that uses the style sheet and template files of another theme – the parent – and can override them.  The basic idea is that instead of modifying the parent files, you simply drop new versions of the files into the child theme folder.

This can be useful in a couple of ways:  1) when you have a theme that you want to tweak slightly  or 2) you’re using a theme that’s updated by the author and you don’t want any of your customizations to be overwritten during updates.  Ian Stewart has a great piece on how he used a child theme to redesign his blog while Benedict Eastaugh offers up some thoughts on the importance of inheriting theme files.

I also talked about the next logical step from these uses of parent and child themes, and that is, for developers and designers in particular to use a parent theme as a kind of framework around which they then build out clients sites.  The idea is that the parent be a barebones theme in terms of design, but contain lots of functionality that clients need over and over again (for example, a series of page templates that provide various formats, such as columns or tabbed content – you know clients are going to want these features).  Then the child theme is where the particular client’s look and unique functionality are created.

There are a number of theme frameworks already available, such as:

• Sandbox
• Hybrid
• Thematic
• WP Framework
• Carrington

But for developers and designers, it makes sense to create your own theme framework, and for that there’s a great series of tutorials by Ryan Imel.

Update: I just came across a piece by Dan Cole arguing the case that making style changes through a child theme is not a good direction to go, while also arguing that theme frameworks is a good idea.  He feels design modification abilities ought to be built into a theme.  I’m going to write a separate piece commenting on his ideas.