What is the most spoken language in the world?

It depends on whether you count native speakers or total speakers, and the answer flips between the two. By total number of speakers (native plus those who learned it as a second or additional language), English is the most spoken language in the world, with well over 1.5 billion speakers, but the striking fact is that the large majority of those are non-native speakers, people who learned English as a second language, because English has become the dominant global lingua franca of business, science, aviation, the internet, and international communication. Relatively few of the world's English speakers grew up speaking it at home; most learned it as the world's common second language.

By native speakers, the people who grew up speaking it as their first language, the winner is Mandarin Chinese, with roughly 900 million to over a billion native speakers, far more than English's native population. Spanish also ranks very high on native speakers, competing with English for second place natively, and Hindi is another giant. So the honest breakdown: Mandarin Chinese has the most native speakers by a wide margin (a reflection of China's huge population), while English has the most total speakers because of its unmatched role as the language people around the world learn in addition to their own. This is why you will see both English and Mandarin cited as the most spoken language, and both are correct under different definitions. A further nuance: Chinese is really a family of related but often mutually unintelligible spoken varieties (Mandarin, Cantonese, and others) unified largely by a shared writing system, so how you count that shapes the numbers too. The clean answer: English if you mean total speakers, Mandarin Chinese if you mean native speakers.