We fell in love with Seth Casteel's dog photos in Underwater Dogs and It's a Puppy's Life, but here he captures something altogether different, and wondrous. The friendships between dogs can be as complex as those between people—with the added factor of sometimes wildly differing sizes—so Casteel avoids interacting with his subjects in favor of observing their natural behavior. Among these 125 page-filling portraits are best friends Dash and Pela (a senior Miniature Dachshund and a Great Dane puppy), Monticello and Gregory (a Newfie and a Pom, and both fluffy), and the threesome Scully, Chess, and Wild (a hound, a collie, and a wolf).