They picked up gold at Beijing, Athens and Sydney, and have been the dominating force in the sport for almost 80 years, winning nine Olympic golds.
Standing in their way in the group stages are 2008 silver medallists USA, bronze medallists Serbia and fourth-placed Montenegro.
The reigning champions also face Host Nation Great Britain and Romania.
In the other group of six are Croatia, Greece, Kazakhstan, Spain, Italy and Australia.
Croatia have recently won the world league competition and Italy are the reigning world champions.
Four teams from each group will go through to the quarter-final stages.
With so many strong teams in the competition, there will be some crucial battles played out in the pool.
The women's competition is made up of two groups of four teams.
Hosts Great Britain line up against Italy, Australia and Russia, while 2008 silver medallists USA will take on Spain, China and Hungary in the group stages.
Reigning Olympic champions Holland failed to qualify for London 2012.
All four teams from each group will qualify to the quarter-finals, so the competition is bound to throw up some surprises.