Claycourt specialist Nadal has never been beyond the third round of the grasscourt grand slam while Roddick has been runner-up the past two years to Roger Federer.
Unlike other grand slams Wimbledon organisers use a formula taking into account past grasscourt performances to decide seedings rather than purely following the ATP rankings.
Nadal is second in the ATP rankings having just won his second successive French Open. It means he cannot meet defending champion Federer, the top seed, until the final.
Roddick, who is ranked five by the ATP, will be third seed at Wimbledon and could therefore meet Federer in the semi-finals.
The top five women's seeds are the same as in the WTA rankings. France's Amelie Mauresmo is top seed, followed by Belgians Kim Clijsters and Justine Henin-Hardenne, Russia's 2004 champion Maria Sharapova and her compatriot Nadia Petrova.
Defending champion Venus Williams is seeded seven, five places higher than her WTA ranking.
China's Li Na is seeded 28, becoming the first player from her country to be seeded in a grand slam singles draw.
No British player is seeded in the men's singles with Greg Rusedski, Andy Murray and four-times Wimbledon semi-finalist Tim Henman all too far down the rankings.
Wimbledon fortnight starts on Monday.
