“I was in love—and leaving in four days.” Leemore, a native New Yorker, was in Paris, of course.

“I met Nicolas at a party in Montmartre,” she tells me. “On our first date, we went to the theater, where he held my hand the whole time. He then took me to dinner, where we kissed in the terrasse as the waiter literally sang to us.”

Such is Paris, where men, Leemore says, take a spontaneous approach to romance—her date with Nicolas was typical of her time there. American men, she said, “simply aren’t romantic.”

That might be true. But French spontaneity is bad news for proprietors of online dating, especially American and British online-dating companies that have struggled to appeal to international consumers. Cupid PLC, the U.K.’s No. 1 dating agency and the owner of Cupid.com, burned a lot of money when it tried to expand its BeNaughty website with becoquin.fr in France and gibsmir.de in Germany. Match.com sold its entire European business to the French site Meetic.com. [Editor’s note: Match.com and Newsweek and The Daily Beast are owned by IAC.]

These companies were sometimes felled by practical idiosyncrasies. For example, Henning Wiechers, from Leading Dating Sites, said many American online dating companies initially offered credit cards as the sole payment method in Europe, not knowing that only 25 percent of Germans own them.

Local attitudes towards online dating can also be difficult to parse. The French don’t really “do” online dating, a Parisian woman told me—that is, aside from AdopteUnMec.com, “which is kind of for one-night stands,” she says. “It’s not OK to use that website.”

Australians take a more relaxed approach to dating. “In Australia, you can never really be sure if you are on a date or you are just hanging out as friends,” says Katrina, an Australian who spent a year in Texas. “In America, you know you are going on a romantic date, because you are asked to do so in this surprisingly formal way.” Another Australian, Andrew, told me that he found it hard to meet new people because of the lack of a formal dating culture. He tried online dating, but he says that it is a taboo for young Australians. “People are really ashamed to try it,” he says. “They won’t admit to it.”

Taiwan offers a more conservative scene. Potential partners are mainly set up through friends, and romance must be found within one’s social circle. “The whole culture of going to bars and flirting with strangers is considered kind of weird,” explains Kevin, who is from Taiwan.

“Without a strong understanding of Chinese users’ behavior, which is influenced by Chinese culture, tradition, and economic development, a foreign competitor would really struggle to get it right,” warns Shang Koo, the chief financial officer of Jiayuan.com, China’s largest online-dating platform.

According to David Evans, an industry consultant and the editor of Online Dating Insider, cyberromance will rapidly develop across Asia and throughout the rest of the world in the next few years, due to increasing Internet access. Mark Brooks, another industry consultant and the editor of Online Personals Watch, predicts that the Chinese online-dating industry alone will generate $350 million in revenue in 2014 and forecasts growth in such developing markets as Russia and Latin America.

That’s why stories of idiosyncrasies and romantic aspirations of the local consumer do not just interest anthropology students. To maximize chances of success, online dating companies have to tailor their websites to specific customs, and uncovering those quirks can require arduous research. Gian Gonzaga, chief scientist for eHarmony, sent out thousands of questionnaires in countries including Brazil, Australia, and the U.S.

“We found Brazilian couples value passion the most,” Gonzaga says. “The importance of similar levels of spirituality is highest in the States.” EHarmony then adjusted its websites’ algorithms to reflect Gonzaga’s findings.

Paul Hollander, professor emeritus of sociology at the University of Massachusetts, Amherst, attributes the popularity of online dating in America to its unique national character. “Americans are a somewhat unusual combination of the romantic and practical. They are great believers [that] if they use the proper methods—in dating or getting rich—they will succeed.”

Sometimes an online-dating company is surprised to find that its product appeals to a demographic it did not originally intend to target. David Evans explained that StepOut originally launched in New York—until it noticed that traffic from India kept rising. Now it has 4 million users there. Indians are accustomed to arranged marriages, and StepOut focused on “friendship,” a term young Indians are comfortable with.

The online-dating industry is continuing to expand its borders, and the science of online matchmaking is advancing in tandem. Helen Fisher, an anthropology professor at Rutgers University and the chief scientist for Match.com, is researching how traits linked with the activities of testosterone, dopamine, estrogen, and serotonin influence attraction—with the goal of facilitating matches between people with similar or complementary brain chemistry.

Fortunately for Match.com, Ficher’s research will be applicable across the globe. “When looking at love across different cultures, our basic biology doesn’t change,” Fisher said. Finally, a romantic thought for Valentine’s Day. Dating behavior may differ internationally, but we are all chemically identical in love.