 <p>The <a href="https://developer.mozilla.org/en/Gecko_DOM_Reference" rel="nofollow">Gecko DOM Reference</a> is pretty complete.</p> <p>For the dark side (IE-specific stuff), there's also Microsoft's <a href="http://msdn.microsoft.com/en-us/library/ms533050%28VS.85%29.aspx" rel="nofollow">HTML and DHTML Reference</a></p> <p>And for cross-browser advice, consult <a href="http://www.quirksmode.org/" rel="nofollow">QuirksMode</a> (thanks Raynos)</p>