Free ebook from Automattic (WordPress.com), WordPress Meet Responsive Design featuring Chris Coyier:
Right now you quite possibly have sites out there in the wild that look like death on one screen or another. And while your trainwreck site turns site visitors away, devices are proliferating faster than anyone can remember what to call them, making your trainwreck site a trainwreck pile up.
Gone are the days of the fixed layout tailored to some imaginary, cramped CRT. And the half way house of fluid layouts are no longer enough when you’re presenting content to people looking at your site through smartphones, tablets, various sized laptops or arrays of gigantic monitors with resolutions of titantic proportions.
That’s where Responsive Web Design (RWD) comes in.