Artificial languages are often classified on the basis of whether they are based on natural languages or are attempts to build a language (or at least the vocabulary of a language) "from scratch". The former type are called 'a posteriori' languages and the latter 'a priori' languages. This is not a strict dichotomy, but rather a spectrum, and there may be no truly a priori languages. However, languages with substantial a priori and a posteriori components have been labelled 'mixed' languages.This book is a survey of several such languages. After an introduction, there are chapters on phonetics, lexicon, morphology, syntax, and semantics. Given that these languages are partly a priori, one might wonder to what extent they conform to universals posited for natural languages, and this is examined with respect to various properties. The languages discussed include Volap=FCk (by far the best known and most successful language of this type), the Blue Language,Gilo, pan-kel, and Vela.