CCP is being rather selective with its invites to DUST 514's ongoing beta test. That said, if you attended Fanfest 2012 last month, you can now redeem a closed beta voucher code and get on with the sci-fi sandbox fragging.
You'll need one of the code cards given out at Fanfest, and you'll need to enter the numbers on the new redeem page at the DUST 514 website. Once you've done so, you'll be placed in a queue to receive your actual beta code via email. CCP says it will begin sending out said codes "very soon, hopefully as early as the week of May 7, 2012."