Enemies

World Government

The World Government views Shanks as a problem and a trouble maker, but realizes he is a man who won't try to change the world by himself. However due to the position he holds, they fear he could get out of hand and are prepared to eliminate him if he ever does. The World Government tolerates his actions until that time comes.Apparently, Shanks and Fleet Admiral Sengoku respect each other. Even as enemies, both the World Government and Red Hair Pirates see a clash between sides as the final option.

Vice-Admiral Garp blames Shanks for poisoning Luffy's mind with ideas about being a pirate when he wanted Luffy to become a Marine.[17]

Buggy
So far, outside of the World Government, the only one who appears to oppose Shanks is Buggy the Clown. Ironically, in their youth Buggy accused Shanks of being too naive and innocent to ever make it as a pirate and yet presently Shanks is a great pirate while Buggy and his crew are very weak in comparison.[18] Yet despite what they claimed to each other, Buggy did not pass the opportunity up to exploit Shanks name and when the two met for the first time in years, Shanks was able to trick Buggy into giving Luffy the Straw Hat back. Buggy then had a go at Shanks for it afterwards while Shanks himself was calm despite Buggy's reaction, indicating that despite their differences the pair's relationship between them is still on a similar ground to what it was in the past, although Shanks has matured. Also, Buggy seems to share Shanks' love of partying.
Yonkou
As his rivals, the other Yonkou are enemies. However, he doesn't want the Marines to parade over the triumph of seeing Whitebeard and Ace dead and takes up the responsibility to give them proper burials.

Marshall D. TeachYet the one Shanks seems to watch out for the most is Blackbeard, who gave him his three scars in a previous encounter.[4] At Marineford, he was exceptionally sharp toward the other pirate. Shanks himself seems to know the potential danger Blackbeard is more so than anyone else.