An application programming interface (API) is a set of rules and specifications that software programs can follow to communicate or ‘interface’ with each other.

As developers are well aware, there are hundreds of APIs out there for doing almost anything you could imagine online. Some are better than others, and some are definitely more useful than others.

Below are forty of the most useful APIs out there. The included APIs will let you do everything from shortening a URL to displaying a book preview on your site to interacting with your Twitter account, and everything in between.

Please share with us which APIs have you found most useful and feel free to recommend others that we may have missed…

When it comes to the creative arts, a fundamental way to better understand the trade is to look to the past.

People in every trade do this, including those in photography, painting, sculpture and architecture. Why should web designers be any different?

Of course, we look to the very recent past through our countless web design showcases. But we can go much further back for inspiration, to the masters of old.

Let’s review some key art movements and the fundamental design principles they embraced. Based on these, we can review current web designs for elements to apply to our own work.

We’ll focus on Western art before the 20th century, and we will highlight only a few movements from among the many that took place.

New WordPress themes are released on what sometimes seems a daily basis.

But not all themes are created equal. Differences in quality become more pronounced in free themes, but there’s even a lot of discrepancies in premium themes, both in terms of visual style and actual code.

Below are more than sixty new WordPress themes released since March. Roughly half are premium themes (ranging in price from around $15 to about $70) and half are free.

If you think there are other themes out there released during the same time period that should have been included, please let us know in the comments! Enjoy the collection…

Every week we tweet a lot of interesting stuff highlighting great content that we find on the web that can be of interest to web designers.

The best way to keep track of our tweets is simply to follow us on Twitter, however, in case you missed some here’s a quick and useful compilation of the best tweets that we sent out this past week.

Note that this is only a very small selection of the links that we tweeted about, so don’t miss out.

To keep up to date with all the cool links, simply follow us @DesignerDepot