Sometimes you can, depending on the broker and the company. I think the rules are something like this (someone correct me if mistaken) If an IPO is the very first time the company has any public debt or stock, then the answer is generally no. If the company already has public debt or some other financing that is public (such as preferred stock, restricted stock, bonds etc), occasionally it is available to short up to and including the first day of trading. It also depends if the underwriter has an over-allotment of shares (they own them in inventory) - and will loan them to you - this would depend on your brokers relationship with the underwriters. That may have changed in the last year or two, but I have shorted IPO's before with a legit borrow within the first 20 days of trading I do not recall if I was able to do it on day 1 but I know after that I have for sure.
Great stuff thx. Reason i asked is because I wanted to know if Shorting Facebook was an option before IPO