Bill Watterson is renowned for his insistence that cartoon strips should stand on their own as an art form, and he has rigorously forbade the use of Calvin and Hobbes in merchandising of any sort. This insistence stuck despite what was probably a cost of millions of dollars per year in additional income for himself and the Universal Press Syndicate. He thought it would cheapen the strip when merchandised.

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Watterson did ponder animating Calvin and Hobbes, and has expressed admiration for the art form. In a 1989 interview in The Comics Journal, Watterson states:

If you look at the old cartoons by Tex Avery and Chuck Jones, you’ll see that there are a lot of things single drawings just can’t do. Animators can get away with incredible distortion and exaggeration [...] because the animator can control the length of time you see something. The bizarre exaggeration barely has time to register, and the viewer doesn’t ponder the incredible license he's witnessed.

In a comic strip, you just show the highlights of action - you can’t show the buildup and release... or at least not without slowing down the pace of everything to the point where it’s like looking at individual frames of a movie, in which case you’ve probably lost the effect you were trying to achieve. In a comic strip, you can suggest motion and time, but it’s very crude compared to what an animator can do. I have a real awe for good animation. (Richard Samuel West, "Interview: Bill Watterson", Comics Journal, February 1989.)

After this he was asked if it was "a little scary to think of hearing Calvin's voice." He responded that it was "very scary," and although he loved the visual possibilities animation had, the thought of casting voice actors to play his characters was something he felt uncomfortable doing. Plus, he wasn't sure he wanted to work with an animation team, as he'd done all previous work by himself. Ultimately, Calvin and Hobbes was never made into an animated series.

Except for the books, two 16-month calendars (1988–1989 and 1989–1990), and a children's textbook, virtually all Calvin and Hobbes merchandise is bootleg, as there has never been any major merchandising of the strip.

Some legitimate special items were produced, such as promotional packages to sell the strip to newspapers, but these were never sold outright.

In keeping with Bill Watterson's reculsiveness, he has almost never given out autographs. Watterson had been known to sneak autographed copies of Calvin and Hobbes collections into bookstores with intent of surprising a few lucky fans; however he put an end to this practice after realizing said books were being sold for top dollar on eBay.

Some bootlegs, such as Calvin and Hobbes on T-shirts depicted as binge drinking or Calvin micturating upon a sports team or corporate logo, are blatantly unauthorized. After threat of a lawsuit alleging infringement of copyright and trademark, some of the sticker makers replaced Calvin with a different boy, while other makers ignored the issue. Watterson once wryly commented "I clearly miscalculated how popular it would be to show Calvin urinating on a Ford logo." Other stickers show a more pious Calvin, such as an image of Calvin kneeling before a Christian cross and praying "Dear God, forgive me for my destructive behavior on other people's windshields". (The drawing is unauthorized, and not by Bill Watterson's hand; Some state, incorrectly, that this image was copied from a strip, published 1992-08-06, where Calvin presents a bowl of pudding as an offering to a TV set.)