Interlingua is a naturalistic language based on the common elements of seven major European languages. As such, its vocabulary is mostly of Greco-Latin origin. The vocabulary is determined by a methodology, not dictated by an organization. Thus, Interlingua automatically evolves along with its "source languages".
Interlingua is meant as a second language for international communication. Because its vocabulary is truly international and its grammar is simple, Interlingua is extremely easy to learn, for both active and passive use, for most people whose mother tongue is a European language.
Interlingua is also the only auxiliary language that is easily understood, whether spoken or written, by hundreds of millions of people who have never learnt it, or never even heard of it. This gives it a unique advantage over other plan-languages such as Esperanto.
Learning Interlingua is also a fun and easy way to gain more insight into the international elements of your own mother tongue.
Interlingua was first published in 1951 by IALA (International Auxiliary Language Association), after almost three decades of professional, paid linguistic research. Unfortunately, one of IALA's major sponsors died just as the project was finished, and the language never received adequate funding for promotion.
Nonetheless, Interlingua has been successfully used in scientific conferences and magazines. Nowadays, the Internet is offering Interlingua new chances.
IALA's Interlingua should not be confused with the "other" Interlingua, also known as Latino sine Flexione, proposed by Giuseppe Peano in 1903.