Ido is an artifical language, based on Esperanto, and created by an international committee in the early years of the 20th Century. It has a simple grammar and largely international vocabulary, making it much easier to learn than national languages. It is intended to be learnt as a second, auxiliary language by people from all over the world in order to improve communication between people of different native tongues.
Such a language is not just a "nice idea", but makes strong economic sense too. In the United Nations there are only five official languages, yet translating documents takes up around a fifth of the UN budget. In the European Union Headquarters there are 11 official languages into which each document must be rendered, taking up almost two-fifths of the administration budget. With ten further countries (and almost as many new languages) set to join the EU in 2004, the problem can only get worse. If there was an international auxiliary language in these organisations and internationally, any document would only need be translated from the original language to the auxiliary language.
Many people ask at this point "But isn't English already the International Language?". Well, only partially. There are several problems with it. Firstly, it's not as widespread as English tourists might like to think; for example across the EU only 47% in total are able to carry on a conversation in English. Secondly, English is far from easy to learn - it has a larger vocabulary than any other language and the orthography (link between spelling and pronunciation) is wildly irregular. Thirdly, national languages are tied to certain countries and picking any national language as an international standard has huge political repercussions.
Any international language should solve the second and third problems above. The current problem is with the first issue: the number of speakers. Even the most widespread auxiliary language (currently Esperanto) has a tiny proportion of the number of speakers that national languages have. This needs to change... I'm trying to "do my bit" by promoting it and providing learning materials for Ido on this website.