Usagi Yojimbo is currently published by
Dark Horse Comics in
TPB form. In the past it has also been published by
Mirage Studios and
Fantagraphics.
A few notes for people interested in
Teenage Mutant Ninja Turtles cross-overs, "Usagi Yojimbo Book Three", published by
Fantagraphics contains an epilogue where
Leonardo is transported back in time.
Leonardo is attacked by outlaws on the same road where Usagi is attacked by ninjas. The two battles merge, and they are the last left standing. They both assume the other is an enemy and attack. They charge each other, and
Leonardo is transported back to his own time just before they can actually strike.
Another cross-over occurs in "Usagi Yojimbo, Shades of Green" published by
Mirage Studios (Which is also contained in the
Dark Horse Comics volume "Usagi Yojimbo, Shades of Death"), where a rat named Kakera transforms 4 turtles into the
Teenage Mutant Ninja Turtles to aid Usagi and his friend Gen.