Russian is a scientific and technological language. Russian accounts for more than 28% of the world's scientific literature. Some of the most important material in physics, geophysics, meteorology, geology, biology, and engineering is available in Russian. Although English is now the main working language in science, Russia has one of the largest communities of scientists in the world. According to the Central Federal Agency on Language Regulation (RAUF), Russian is an official language in 42 countries. It is one of the four national languages in India and Israel. In addition, many people around the world speak Russian as a second language. This makes Russian the most spoken language without regard to population size. Currently, there are about 20 million native speakers of Russian worldwide, with more than 100 million people having some knowledge of the language. The most populous countries by number of Russian speakers are Russia and Ukraine. However, the majority of these speakers are not native speakers; they learned the language from parents or caregivers during childhood. Native speakers are mainly found in Russia, Ukraine, and several other former Soviet states. The modern Russian language is a descendant of the Old Rus' language that was first spoken in the territories of present-day Russia in the early 10th century. Over the next few centuries, it became the language of administration, literature, and religion in the growing state known as Kievan Rus'.