Justin Bieber has finally turned 18, and we're counting down his 18 greatest moments so far in honor of the occasion. This week, we kicked things off by looking back on some of the highlights, from Justin crashing this year's Oscars to his headline-making romance with girlfriend Selena Gomez.

In the latest installment of our Bieber birthday countdown, we pick up with #13 to #6, narrowing down the early achievements that helped shape the teen into the pop superstar we know and love. We'll celebrate this week until the final reveal on Justin's big day on Thursday. What will be the #1 moment?

13. Bieber Drops "Baby" Video
In February 2010, Justin dropped his star-making "Baby" video. Proving he had lots of swag, he enlisted Ludacris and Drake to appear in the bowling-party-themed clip, which featured a romance with his pretty leading lady. The video also displayed Bieber's budding persona as a charming pop Romeo that no girl can resist.

"It starts off, I really like this girl, but we didn't [get] along; we couldn't be together," he told MTV News while shooting the video. "Basically, I want her back and [I'm] kind of going through the whole thing. I'm chasing her around, trying to get her, and she's kind of playing hard to get, but I'm persistent. I keep going."

12. Justin's Voice Changes
No one is immune to puberty, and that includes teen stars. As Bieber continued to mature before our eyes, his voice also took a turn for the manly. But he wasn't too worried about it. "Everyone's voice changes. Puberty is a natural thing," Bieber said in 2010. "I have the best vocal coach in the world and we're working on my voice and doing what I need to do. It's not like as soon as you hit puberty you stop singing. Usher is the best mentor in the world and he survived puberty. He tells me what to do, what not to do."

11. Bieber Goes Hip-Hop
Between his rap persona, Shawty Mane, and getting love from a number of A-list hip-hop pals like Kanye West, Luda, Drake and Lil Wayne, Bieber has proved that swag is more than just a hashtag to him. This kid can legitimately hang with some of the hardest guys in the game — and hold his own.

10. 2011 Grammy Awards
At last year's Grammys, Bieber seemed poised to take home a trophy, but he famously lost in the prestigious Best New Artist category to Esperanza Spalding. He shook off the loss, though, and vowed that one day he would take home Grammy gold. He's set to release his next album, Believe, in 2012. Grammy voters, take note!

9. Bieber Drops My World 2.0
For his second EP, My World 2.0, Bieber upped the ante when he enlisted folks like The-Dream to produce. While the record was released in March 2010, only months after his first EP, My World, the follow-up managed to eclipse the original thanks to memorable songs like "U Smile," "Baby" and "Up." 2.0 helped spark the frenzy known as Bieber Fever. The teen star even scored an MTV special on the series "Diary."

8. Bieber Goes Under the Mistletoe
He invited us all to premiere his video for "Mistletoe," the lead single off his holiday-themed Under the Mistletoe. When he sat down with MTV News for his "MTV First" interview, he talked all about shooting the video in Nashville, his desire to make a cool Christmas album and getting the chance to work with heroes Mariah Carey and Boyz II Men.

7. Fans Welcomed to My World
In 2009, Bieber dropped his first EP. Full of sugary-sweet pop, the songs launched him from viral Internet sensation to full-on star. The album was rife with puppy-love tracks that displayed Bieber's ear for melodies and recalled some of the great pop music of the past from stars like New Kids on the Block and even Michael Jackson.

6. First Film, 'Never Say Never,'
Released Bieber's first foray into the world of big-screen blockbusters came courtesy of a 3-D film, "Never Say Never," that served as a documentary and a concert film. It addressed any of his haters with in-depth interviews with the folks who know him best and Bieber himself, who recalled his personal hardships before making it big. If that wasn't enough for the Beliebers, it also featured a 3-D Bieber shaking his floppy hair around.

Copyright : MTV.com