London - Serena Williams and Novak Djokovic were named the women's and men's players of the year by the International Tennis Federation (ITF) on Tuesday.
Both won three of the four Grand Slams in 2015 and are well clear in the world rankings.
Williams, who was named 'ITF World Champion' for the sixth time, won five titles throughout the year, finishing with a 53-3 win-loss record.
After winning Wimbledon in July she also held all four Grand Slam titles at the same time for the second time in her career, which she previously dubbed a 'Serena Slam' in contrast to a calendar Grand Slam.
"It means a lot to me to be named the ITF World Champion for the sixth time. I am proud to have achieved my second Serena Slam, in what has been an amazing year for me," she said in an ITF statement.
Djokovic, who finished the year as men's number one for the fourth time, won the award for a fifth time.
He managed a career-best 11 titles and finished with an 82-6 record.
He got even closer to the Grand Slam than Williams, who was beaten in the US Open semi-finals, as he only missed out on a first Roland Garros crown in the final against Stan Wawrinka.
"My season was the best of my career with many highlights. It inspires me even more to keep on going, and I hope to continue to play at this level in 2016," he said.
India's Sania Mirza and Martina Hingis of Switzerland were named the women's doubles champions with Dutchman Jean-Julien Rojer and Horia Tecau of Romania picking up the men's award.