The purpose of this paper is to offer an exemplification of the author's philosophical viewpoint by using Mozart's music: nihil reputare insulatum ('to consider nothing isolated'). In other words, by placing Mozart's music in a wider frame of reference, the author tries to show that his musical works as well as small fragments of his music cannot exist without any relations with other musical texts. Such relations between musical texts are defined as 'intertextuality'. In this connection, the word 'text', like its Latin form 'textus', should be understood as referring to units of musical works on various levels. In order to show the richness of intertextuality which Mozart's music has historically build up with other musical texts, the author proposes the following five techniques of intertextuality:1. variation; 2.transcription; 3.juxtaposition; 4.quotation; and 5.parody. 1.Variation. In principle, variations have intertext uality relationships with their themes. Mozart's famous variation K.265 is related to the French folk song "Ah, vous dirai-je, maman" which was used as the theme of this variation. 2.Transcription Here, the transcription means various ways of transposing a musical text to other media, e.g. to other instruments. Transcribed musical texts are necessarily related not only to their original text, but also to other transcribed texts deriving from the same text. 3.Juxtaposition. As in the case of Luciano Berio's "Sinfonia", the juxtaposition here refers to various ways of performing plural musical texts simultaneously. It is quite conceivable that someone will juxtapose one of Mozart's musical text with any other musical texts in order to establish intertextuality relations among them. 4.Quotation. Zofia Lissa defined the musical quotation as follows:"utilization of pre-existing literary and musical phrases (antefacta) in a context which differs from the original one". In order to distinguish quotation from other from other techriques of intertextuality, this author proposes an additional condition to Lissa's definition:the antefacta of quotation can be judged as quotations, if and only if they are diachronically isdated from their adjacent parts. Based upon this additional condition, he examines various examples of quotations in Mozart's texts as well as in later works quoting Mozart's texts. And 5.Parody. A parody work has intertextuality relations with another musical text, i.e. its target. Mozart's ensembles work "A musical joke" (K.522) is related to clumsy ways of music making found in peasant ensembles in terns of the fifth technique of intertextuality, parody. The final part of this paper discusses the significance of reception in the formation of intertextuality in general.