The Internet has known a very fast evolution, going from the Web 1.0, i.e., the traditional Web where users are merely consumers of static information, to the more dynamic Web 2.0, known as the Social or Collaborative Web, where users produce and consume information simultaneously, and heading toward the more sophisticated and eagerly anticipated Web 3.0, better known as the Semantic Web: extending the Web by giving information well defined meaning so that it becomes more easily accessible by human users and automated processes. This paper briefly describes the evolution of the Web towards the Semantic Web (3.0), providing an overview of the various technological breakthroughs contributing to this evolution, covering: knowledge bases and semantic data description, as well as XML-based data representation and manipulation technologies (i.e., RDF, RDFS, OWL, and SPARQL). We also present the main application domains characterizing the Semantic Web, ranging over information retrieval, information extraction, machine translation, content analysis, and lexicography, and discuss some emergent and future directions aiming at improving Web data accessibility and performance.