Check out the NY Times article "INSIDE ART: Whitney Chooses Biennial Curators" by Carol Vogel on December 12, 2008.
Quoting from the article: "For the next biennial, which will open in March 2010, the museum has paired an Italian-born curator with an international reputation with a homegrown senior curatorial assistant." Read more.
If you're not familiar with the show, visit the Whitney Biennial 2008 on the web.
From what I understand, the work for previous Biennial's was chosen by Whitney curators who found the work to be exhibited. For a number of years, the Whitney also had artist submission requirements posted on their website, if an artist wanted to send images for consideration for the Biennial. I have no idea if anyone who submitted work on their own was ever included in the show, but it was nice on my end at least, to be able to send images and hope someone looked at them. I don't know if they'll offer that again for 2010, but it's worth checking their website every now and then to see if it's posted.
