Djokovic won a career-best 11 titles in 2015 and topped the year-end rankings for the fourth time.

The Serbian won Grand Slam titles at the Australian Open, Wimbledon and US Open and was runner-up to Switzerland’s Stan Wawrinka at the French Open.

He was in commanding form on all surfaces, boasting a career-best 82-6 win-loss record for the year.

"It is an honour to be named ITF World Champion for the fifth time," said Djokovic.

"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."

Williams came within two matches of achieving the Grand Slam in 2015, winning the Australian Open, French Open and Wimbledon before losing her US Open crown with a shock defeat at the hands of Italy’s Roberta Vinci in September.

The American held all four Grand Slams at the same time for the second time in her career following her success at Wimbledon.

She won five titles in 2015, and finished number one in the year-end rankings for the fifth time on the back of a 53-3 win-loss record.

"It means a lot to me to be named the ITF World Champion for the sixth time," said Williams.

"I am proud to have achieved my second Serena Slam, in what has been an amazing year for me.

"Thank you for this recognition and for the undying support of the tennis community."

Martina Hingis of Switzerland and India's Sania Mirza have become women’s doubles world champions, while Jean-Julien Rojer of The Netherlands and Romania’s Horia Tecau have been crowned the men’s doubles World Champions.

Hingis and Mirza only joined forces in March but proved a force to be reckoned with in 2015, winning Grand Slam titles at Wimbledon and the US Open, along with a seven further tournaments.

They won their last 22 matches from the start of the US Open through wins in Asia in Guangzhou, Wuhan, Beijing and the WTA Finals in Singapore, ending the year with a 55-7 record.

Rojer and Tecau, meanwhile, enjoyed a breakthrough season which saw the pairing capture their first Grand Slam title at Wimbledon.

They also won in Rotterdam and at the ATP World Tour Finals in London, landing the season-ending title without losing a set to clinch the year-end number one doubles team ranking.

Hungary's Dalma Galfi and Taylor Fritz of the United States have been named ITF junior world champions.

The ITF wheelchair world champions are The Netherlands' Jiske Griffioen and Shingo Kunieda of Japan, who becomes men’s champion for the seventh time.

Galfi is the first-ever Hungarian player to receive the ITF world champion honour in any category.

In a competitive girls' season on the ITF junior circuit, the 17-year-old won the US Open and secured the year-end number one ranking in the very last tournament of the year.

Fritz is the first American boy to be named ITF junior world champion since Donald Young in 2005.

The 18-year-old reached two Grand Slam junior singles finals in 2015, winning the US Open, and after taking over the number one ranking in June, he held on to the top spot for the rest of the season.

As ITF world champion for the seventh time, Kunieda is now the most decorated player in the wheelchair men’s category.

The Japanese had another outstanding season, collecting seven titles on the UNIQLO Wheelchair Tennis Tour, including all three Grand Slam singles titles, and achieving a 30-2 singles win-loss record.

Griffioen had a breakthrough in 2015, winning her first Grand Slam wheelchair singles title at the Australian Open, and following that up with a second triumph at the French Open. 

Having been ranked continuously in the top five since September 2010, the 30-year-old finally reached the top spot in June and stayed there for the rest of the year.

The ITF’s selection of its senior world champions is based on an objective system that considers all results during the year, but gives special weight to the Grand Slam tournaments, and two ITF international team competitions, the Davis Cup and the Fed Cup.

The ITF World Champions will receive their awards at the 2016 ITF World Champions Dinner in Paris on May 31, during the French Open.