Katy Perry bikini pictures

Katy Perry turns 28 today! It's been quite a year for Katy. She had nothing but success when it came to her career, having multiple singles off her Teenage Dream album make it to the top of the charts. She also embarked on an around-the-world tour and released her first movie, Katy Perry: Part of Me. She dealt with the breakup of her marriage to Russell Brand, but she may have found love again with new guy John Mayer. Katy was even able to celebrate John's 35th birthday earlier this month!

For Katy's big day, we've rounded up 28 of her sexiest moments. Click through to see them all — and happy birthday, Katy!

Katy Perry spent yesterday afternoon in her bikini at Raging Waters in San Dimas, CA, with a group of friends. Katy is enjoying some downtime after wrapping a worldwide tour to promote her movie, Part of Me, which most recently took her to Brazil. John Mayer and Katy Perry have been spotted out together on a couple of dates recently, and went to a house party together on Saturday night, but he didn't join her at the water park. Neither she nor John have commented on their relationship, which is one of Katy's first since her split from Russell Brand. She was also linked to the guitarist of Florence + the Machine earlier this year, but the pair apparently cooled off early this Summer.

Katy Perry wore a bikini to lounge by the pool with friends, sip drinks, check her iPhone, and work on her tan in Miami on Friday. She has been in Florida for a few days. Katy was spotted reading Robert Pattinson's BlackBook issue during another poolside afternoon earlier this week. Katy is not among the many celebrities who commented publicly about the Kristen Stewart cheating scandal, though she is good friends with both Robert and Kristen. Katy's own love life is back in the headlines as well, since she was reportedly spotted getting close to John Mayer recently in LA.

Katy Perry slipped into a black bikini to lounge poolside at Miami's SOHO Beach House today. She was reading the latest issue of BlackBook Magazine, which features her friend Robert Pattinson on the cover. Katy, who is friends with both Rob and Kristen Stewart, has been spotted spending time together with the couple this Spring and Summer, though she is not one of the celebrities who have weighed in on the Kristen Stewart cheating scandal.

Katy has been enjoying a break since promoting her 3D film Katy Perry: Part of Me earlier this Summer. The film didn't draw in big bucks at the box office, but it was relatively cheap to make. Katy nonetheless took home the choice summer movie surfboard at Sunday's Teen Choice Awards. It also seems Katy may have some news in the romance department. It's rumored that Katy Perry's dating John Mayer. The pair were reportedly spotted on a date at LA's Soho House last week, though neither star has addressed the stories publicly.

A bikini-clad Katy Perry spent her Christmas Day hitting the beach in Hawaii with a few good friends. Katy was without husband Russell Brand, though she looked to be surrounded by loved ones. 2011 was another year of outrageous style for Katy Perry as she took her smash hit album Teenage Dream around the world including, most recently, a turn hosting SNL. Katy and Russell's demanding work schedules means a lot of time apart, though they have denied all rumors of trouble in their relationship. Russell and Katy got engaged two years ago on New Year's Eve, so perhaps they'll find a way to be together for that milestone.

Katy Perry slipped into a pink polka-dot bikini and headed to the pool in Miami on Tuesday. She's in Florida visiting her husband, Russell Brand, who is currently shooting the musical comedy Rock of Ages alongside Tom Cruise, Alec Baldwin, and Julianne Hough. Katy enjoyed a short break from her California Dreams tour, which resumes tonight with a show in Pittsburgh, and it seems she also took the opportunity to test out a new red hair color. Her form was also on display earlier this week inside the pages of Rolling Stone — the magazine featured its latest Katy Perry bikini spread.