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Up util now, I've used Paul Irish's bulletproof font-face sytax
But I was just looking at support for .woff and .woff2 files on caniuse and it says woff is supported in IE9+. Most articles on this topic are from around 2009, which at the time of this writing was a full 7 years ago. Do we really need to keep declaring ttf, otf, eot, and svg when woff now enjoys such wide support?
Short answer: no.EOT is only relevant for IE8 and below (although as trivia: all the way down to IE4. IE actually pioneered webfonts), and SVG fonts as technology were abandoned because the limitations were insane once real webfonts started to become available. As of 2016 you just need WOFF. And WOFF2 if you want to take advantage of the newer better version of WOFF that only just became a w3 recommendation.
Also note that as of January 12th 2016, Microsoft ceased support for IE8 and below, with limited support for IE9: they will now only support the latest available browser for each still supported OS, meaning that IE9 is no longer supported for Windows XP, because XP is itself no longer supported, but is technically still—begrudingly—supported until Vista SP2 and Server 2008 R2 reach the end of extended support in 2017 and 2020, respectively. Of course, for Windows Server 2008 webfont support is irrelevant, and most businesses that still use an old version of Windows skipped Vista, being either on Windows XP (at their own peril) or Windows 7 (which we can pretty much expect to all become Windows 10 in July of 2016, the 29th of which is the last date people can upgrade from 7/8.1—but not 8—to 10 for free).
As for TTF/OTF, don't use them online. Even though WOFF is just a thin wrapper around a TTF/OTF file (with optional compression), yielding a byte-for-byte identical file when the WOFF is decoded, TTF/OTF are universal (OpenType-supporting system) fonts, and so are scrutenized more, especially by versions of IE. Using WOFF, which as a filetype makes it explicit this is a web (open) font (format), a "laxed" form of scrutiny means that some fonts that would fail a TTF/OTF verification check may still work just fine as webfonts (due to the fact that not all required-for-universality OpenType data is necessary for a font to work in just a web context)
In conlusion: hurray for the march of progress, just use WOFF.