Twenty years ago, few parents swaddled their babies, white noise for sleep was a rarity, and the 5 S’s, calming reflex and fourth trimester were as unknown as the dark side of the moon. That all that changed in 2002, when a new book and video, The Happiest Baby on the Block were “born” and taken home by excited new parents. Fast-forward 20 years, and dog-eared copies of what has become a parenting classic are on nightstands across America and around the world. This friendly and helpful guide by our founder, Dr. Harvey Karp, has quite literally, changed our basic understanding of how to nurture babies. It has sold millions of copies—in dozens of languages—and has spent two decades being celebrated on the parenting bestsellers list. And, most importantly, Happiest Baby has given countless parents the gift of feeling competent, prepared, and successful. No wonder The New York Times, in their description of the amazing revelations shared in The Happiest Baby on the Block, proclaimed, “Roll over, Dr. Spock!”

So, please join us in commemorating some of the many ways in which this seminal work has introduced wonderful new ideas to the ancient art of parenting! Dr. Karp and The Happiest Baby have:

Popularized the Fourth Trimester 

Twenty years ago, Dr. Karp brought into common use the basic idea that babies are best thought of as being born three to four months before they’re technically “ready for the world.” He helped parents understand that babies must be born before they can even smile, coo, or lift their heads because their brains are so big! If they waited to be fully developed their heads would be too big to get out. And because newborns are still not finished “cooking,” they need us to give them a womb-like environment after birth to feel safe and comforted. That period of intense caregiving—the missing fourth trimester—was popularized by Dr. Karp. And in 2021, the term had so thoroughly penetrated our contemporary culture that the Merriam-Webster dictionary included it in their newest edition as an official part of the English language.

Discovered the Magical Calming Reflex

Many parents have noticed that bouncy car rides and the rumbling of a hair dryer can quiet their baby’s cries. In fact, for thousands of years, parents have used swaddling, rocking, and shushing to calm babies. But it was Dr. Karp who first realized that these work by turning on previously unknown innate response, the so-called calming reflex. When parents imitate the rhythmic sensations of the womb, this is almost magical reaction often calms crying in seconds—and improves a baby’s sleep.

Invented the 5 S’s

To turn on the wonderful calming reflex—and help parents and babies sail through the fourth trimester—Dr. Karp created a simple mnemonic to help parents remember the key steps for imitating the soothing rhythms of the womb: the 5 S’s (swaddle, side-stomach position, shush, swing, and suck). Today, thousands Happiest Baby educators have been trained to teach the 5 S’s in hospitals, teen parenting clinics, child abuse prevention programs, WIC centers, inner city parent groups, military bases, and more across America and in many other nations. 

Ignited the Swaddle Revolution

For over 100 years, the ancient practice of swaddling fell out of favor in the Western world. It was considered old-fashioned, and parents were taught that babies needed “freedom.” But, in 2002, The Happiest Baby on the Block began teaching parents that for the entire fourth trimester fussy and sleeping babies needed the womb-like security of snug wrapping to help restrain their startles and uncontrolled arm jerks. At that time, if a new parent wanted to buy a swaddle blanket, they’d be hard-pressed to find one. Even the muslin stand-bys were nowhere to be found. But once the 5 S’s wave started, the momentum could not be stopped. Right now, baby swaddles are a registry must-have. Heck, the practice has become so ubiquitous that The Happiest Baby and swaddling even showed up in a clue on Jeopardy!

Harnessed the Power of Video  

When the book launched, Dr. Karp also put out a video to help parents master the nuances of the 5 S’s. Back in the ancient days of DVDs—pre-streaming, pre-YouTube, pre-everything available on your phone—Dr. Karp brought parents one more game changer. To date, it remains the most watched child-rearing video of all time. (The Happiest Baby on the Block video is now available to stream.)

Introduced Revolutionary Ideas on Raising Toddlers

Finally, kids do come with instructions! More than just the top baby guru, Dr. Karp created a new approach for parents to become toddler whisperers (for kids 8 months to 5 years). Drawn from 30 years of pediatric practice (caring for families in need to families of celebs like Madonna and Larry David), his bestselling The Happiest Toddler on the Blockhelps parents learn how toddlers think. The book and video introduce a dozen surprising techniques that can quickly soothe tantrums and teach little kids be more patient and cooperative. For example, his novel talking tip, Toddler-ese (another now-ubiquitous “Harvey-ism”), is a special language style to acknowledge feelings and boost emotional resilience in three simple steps: short phrases, lots of repetitions, and mirroring one-third of a tot’s emotions non-verbally in your tone of voice and face/body gestures. (Dr. Karp’s third landmark child behavior guide is The Happiest Baby Guide to Great Sleep, this time offering innovative sleep solutions, like Twinkle Interruptus, for kids from birth to 5 years.)

Created the Amazing SNOO Smart Sleeper 

We have all heard “it takes a village” and for the entire history of humanity (until 100 years ago) parents had their extended family to lean on. But today, many fall for the big lie that normal parents shouldn’t need help, they just happily work around the clock…then post smiling photos on Instagram. In 2016, Dr. Karp launched his responsive baby bed, SNOO. Just as The Happiest Baby ideas revolutionized our ideas of the needs of babies in 2002, SNOO is revolutionizing infant sleep.

After all, SNOO embodies the key sleep components of the renowned 5 S’s. SNOO swaddles babies safely on their backs, delivers critical white noise (the “shush” of the 5 S’s), and gently rocks Baby back and forth (the “swing” of the 5 S’s) further copycatting the womb. Not only has SNOO helped babies all over the globe clock nearly 500 million hours of sleep, in 2023 the Food and Drug Administration granted SNOO De Novo Authorization for its ability to keep sleeping babies safely on their backs! (For important safety information visit

That’s the amazing more than 20-year legacy of America’s most trusted pediatrician and his groundbreaking parent guides. Thank you all for trusting Dr. Karp, reading The Happiest Baby on the Block and his other books, and keeping the momentum going after all these years! We can’t wait to see what he comes up with next!

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Disclaimer: The information on our site is NOT medical advice for any specific person or condition. It is only meant as general information. If you have any medical questions and concerns about your child or yourself, please contact your health provider.