The course will be divided into three parts. In the first, introductory part, the relationship between human language and communication and languages as instruments of communication will be briefly discussed. To this purpose, some general notions of semiotics will be provided, and a classification of the different types of signs, with a special focus on the linguistic sign, and the main models of the communicative act will be presented. The second part of the course will be devoted to linguistic variation and the study of languages as diasystems: some central issues in sociolinguistic investigation will be addressed, such as the study of the dimensions of linguistic variation, the interaction between language change and variation, and the dynamics of language contact, with a special focus on the categories of analysis helpful for the study of new language varieties related to the most recent means of communication. Finally, the third part of the course will be dedicated to the relationship between linguistic analysis and digital communication, with particular (though not exclusive) reference to the Italian situation. We will analyse the problems related to the placement of digital varieties within the linguistic diasystems and the role of the Web as a source of linguistic data and a privileged field of investigation on the phenomena of ongoing language change.