It's all about the rankings
In the early years, anyone who paid the entry fee, initially one guinea, could take part in The Championships. However, by 1919 interest was so great the All England Club had to be selective. The entry list is now largely determined by the rankings organised by the Association of Tennis Professionals and the Women’s Tennis Association.
As with the other Grand Slams a total of 256 men and women compete in the singles competitions, 128 of each gender. At Wimbledon there are slight differences in who qualifies. In the gentlemen’s singles the leading 104 men, according to the ATP rankings at the cut-off point (around six weeks prior to The Championships), are guaranteed a place. In practice, players ranked lower are likely to be included due to some higher-ranking players being absent with injury.
Another 16 places are on offer through Qualifying, which takes place at the Bank of England Club, in nearby Roehampton, the week before The Championships. That has its own 128-place draw. A further eight players are awarded wild cards. As with the other majors several of these usually go to players from the host country, often young ones of promise. Others may be awarded to crowd favourites or renowned players who have dropped out of the rankings due to injury. Goran Ivanisevic was a wild card when he became Champion in 2001, the only player ever to do so.
The ladies' singles provides direct entry to the leading 108 WTA-ranked players, has 12 places available through Qualifying, and awards eight wild cards. Two wild cards have reached the semi-finals, Jie Zheng (2008) and Sabine Lisicki (2011).