ON the dust jacket of Patrick McDonnell’s new book Wag!, we see a picture of a Jack Russell Terrier in place of the traditional author photo.

   This is Earl, the real-life inspiration of Mutts, Mr. McDonnell’s internationally syndicated comic strip that Peanuts creator Charles Schulz called “One of the best comic strips of all time.”

   Wag! is “a tribute to my dog Earl,” Mr. McDonnell says via telephone. “I always felt that if I could capture his joy and spirit in my work then I was doing my job.”

   Wag! celebrates life’s joy by asking a question Mr. McDonnell and his wife have been pondering for years: “What makes Earl’s tail wag?”

   Food, play, belly rubs — Mr. McDonnell distills the source of happiness to one concept, the thing that makes every dog’s tail go fwip and fwap and every person’s heart go pitter patter. And Mr. McDonnell allows no one other than Earl’s best pal, Mooch the cat, to deliver the message.

   In Wag! (Little, Brown and Company, $15.99), Mooch is constantly interrupting the story, a device that the author, who will appear at jaZams in Princeton Nov. 28, devised after reading to so many first and second graders. Children ask wonderful questions, Mr. McDonnell says, and they’ll interrupt a reading for many things, from airing aimless thoughts to requesting permission to visit the bathroom. “You never know what they’re going to say,” he says. “That’s true of Mooch too.”

   Through their misadventures in and around a New Jersey suburb, Mooch and Earl have been entertaining and teaching readers since 1994. Mr. McDonnell, a Middlesex resident who grew up in the state, says he never thought his strip would be seen around the world. He has more than 20 books in print, many of them celebrating the simple pleasures of nature and friendship.

   ”I think my books and my comic strips are about trying to stop and smell the roses,” says Mr. McDonnell, who has compared the effect of a Mutts comic strip to that of a Zen koan or parable. Guardians of Being (New World Library, $18), Mr. McDonnell’s recent collaboration with the spiritual teacher and author Eckhart Tolle, acknowledges Mutts’ spiritual nature.

   ”I found ‘The Power of Now’ when it first came out and was moved by it and influenced by it,” he says of Mr. Tolle’s 1999 best-selling book. “Over the years my wife and I continued reading his books, listening to his audio tapes and watching his DVDs. His message is very similar to the message of ‘Mutts’ — letting nature help you find that inner peace.”

   He began creating Guardians of Being, which he views as a companion piece to Wag!, by choosing a selection of Mr. Tolle’s quotes that address animals and nature and matching them to his drawings. After Mr. McDonnell produced a dummy book, the two men collaborated, amending words and pictures. The result is a charming hymn to a quiet, peaceful mind — the kind of mental state Mr. McDonnell tries to achieve while working.

   ”I love making art,” he says. “To me it’s a meditation. It’s intuitive. It just feels right. When you do these stories, you have to get out of the way and let your ideas come. You’re sort of a servant to the idea. There’s a lot of letting go.”

   In pursuit of letting go, he puts in a lot of time, working seven days a week from 5:30 a.m. to dinnertime, he says, calling his schedule “farmer hours.” It must be said, though, that some of this time is simply spent watching birds from his home studio, which overlooks an acre of woods. “I call this work,” he says. “I love birds, how free they are. Birds are a big part of ‘Mutts.’”

   Birds are also central to his 2008 book, South (Little, Brown Young Readers), the wordless and remarkably tender story of a lost bird. Picture books were always part of his ambition, Mr. McDonnell says. But before he began adding them to his resume, he simply wanted to create animal characters that, despite being able to talk, were recognizable as pets.

   ”I wanted people to bond with them like their own pets,” he says. “I was aware of trying to see the world through their own eyes. Slowly I became aware of how tough it is for them on this planet.”

   A member of the board of directors of The Humane Society of the United States, Mr. McDonnell launched Mutts “Shelter Stories” in 1998, which presents the stories of shelter animals waiting for homes. These strips, meant to inspire potential pet owners to adopt from shelters instead of buying from stores, run for a full week every year. “Unfortunately I could do one every day of the year,” says Mr. McDonnell, a vegetarian. Of all his work, he has said he is most proud of “Shelter Stories.”

   The following year Mr. McDonnell introduced Mutts readers to his new voice for animal advocacy, an orphan kitten named Shtinky Puddin’ (or Jules) who is obsessed with saving endangered tigers. Jules starred in Mr. McDonnell’s Hug Time (Little, Brown Books for Young Readers, 2007), in which the cat travels the world hugging every creature he meets. Another recurring character, the perpetually tethered Guard Dog, often appears to remind readers why it’s wrong to chain a dog. “What’s nice about the comic strip is that it’s like life — it just grows,” says Mr. McDonnell, later adding that a Mutts movie may be in the future.

   Despite writing from a perspective of advocacy, Mutts rarely if at all comes across preachy or condescending. The tone remains playful and often deceptively light, appealing to our better nature. “I’m such a big comic fan,” Mr. McDonnell says. “My first goal is to do a classic comic strip. Those strips brought so much joy to me. My main goal is to try and give some of that joy and for people to feel good about it.”

   A student of art and comic history, Mr. McDonnell cites Peanuts, Krazy Kat, Little Nemo and Popeye as “constant inspiration.” But it’s the animals in Mr. McDonnell’s life that provide the daily fodder he transforms into art. He and his wife live with their formerly feral cat, MeeMow, the still feral cat Not Ootie and a new Jack Russell Terrier named Amelie, who was adopted nearly two years ago after Earl died. He was around 19 years old.

   ”Right now as we speak, Amelie is throwing a ball at me every five seconds,” Mr. McDonnell says. “I’m always laughing at what she may be thinking.”

   He has begun to incorporate Amelie’s “little doings” into Earl’s life on the page. Readers may soon see a new character based entirely on her.

   ”What’s funny about doing a comic strip is that you do it day by day,” Mr. McDonnell says. “There’s no master plan. Characters come and go. Some stick and some don’t. Most of the time I feel like I just started ‘Mutts.’ I’m still excited about what can happen in the strip.”

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  Mutts creator Patrick McDonnell will sign copies of Wag! and Guardians of Being at jaZams, 25 E. Palmer Square, Princeton, Nov. 28, 3-5 p.m. Pop-up book author Chuck Fisher will also appear. Free. 609-924-8697; www.muttscomics.com