The World Mornington Crescent Championships have technically been held annually since 1836, although only since 1910 have they been truly open to all comers on the basis of world ranking and qualifying tournaments: Mornington Crescent was one of the first competitive games to stop recognising the difference between amateurs (who could compete in the World Championships) and professionals (who previously could not, as playing for money was frowned upon.) The first World Champion in the Open era was Sydney Hall, who was to win seven times. Mrs Trellis holds the record number of victories (17), and Tibor Hugo the record number of consecutive victories (10).
Since 1929, the World Championships have consisted of more than one event: the All-In championship was added that year, and the championships were expanded to include Team (4-player) and Pairs events following the Second World War. To win (or be on the winning team in) all four events in a single year is referred to as a Grand Slam: Mrs Trellis has done this 12 times - her nearest challenger in this regard, Ruttsborough, only three (mainly due to the fact that he seldom played in team events.) The IMCS World Championships are the only championships that incorporate all four of the above: many other Grandmaster-level tournaments miss out the Pairs event, some have a Pairs but not a Team, and some are still only a Singles and an All-In, while others tend to tack a Pairs on to a Team championship and not include a Singles although they may or may not include an All-In at the end.
It should be noted that the Team event in the World Championships is not considered the premier event in Team Mornington Crescent, owing to (a) the existence of a separate World Team MC competition, and (b) the fact that each Team must have at least 50% of its membership made up of people who are in the Singles draw. (The same is true in Pairs, where at least one member of the Pair must be in the singles championship.) Nevertheless, victory is still considered extremely prestigious in any event of the World Championships.
In 1977 they were expanded yet again, to include Under-18 sections for Singles and Teams (although this is not so highly rated, owing to the fact that players who compete in the main championships cannot also compete in the U-18 section: thus removing all real prodigies from the junior division.)