written and illustrated by Eric Carle
Original: 1961
Re-illustrated edition: 1987

I can't believe that I've been a children's librarian for over 20 years and only noticed about a year ago that the illustrations had changed from the first to the current editions of this book.  Original illustrations are in the left side column. The Re-illustrated version is on the right.
In The Art of Eric Carle, the artist explains, “In Brown Bear Brown Bear What Do You See?, I used plain commercially available tissue papers, which come in about forty shades. After that book, I decided to give these hues more texture and color.  So I began to paint with all kinds of brushes,
finger-paint, splash and splatter onto these colored tissue papers.  Then I found out that these commercially available color-hued papers began to fade in the sun. Now I paint on plain white tissue papers. These by-me-prepared tissues become my palette.”

Several of his books have been re-illustrated over the years, including The Very Hungry Caterpillar.   In The Art of Eric Carle, he gives the reason for re-illustrating the book Pancakes, Pancakes  “Twenty years ago my Pancakes Pancakes was published only to go out of print within a year or two. One of my publishers recently wished to reissue this book. I decided to redo the illustrations when I realized that some of the original pictures had been damaged or lost, and that the reproduction methods have improved quite a lot since then.” We can surmise, then, that this is the reason he re-did the art for so many of his books.

Re-illustrated by Eric Carle:
Brown Bear, Brown Bear, What Do You See?  1967; re-illustrated in 1970
The Very Hungry Caterpillar 1969; re-illustrated 1985
Pancakes, Pancakes 1970; re-illustrated 1990
The Tiny Seed 1970; re-illustrated 1987
Walter the Baker 1972; re-illustrated 1995
Have You Seen My Cat 1973; re-illustrated 1987
The Mixed Up Chameleon 1975; re-illustrated 1984

Which one do I like best?  Considering that I didn't even know until a year ago that there was any difference between the two, you could say it was a draw. But comparing the two... I kind of like the original best.