The Web has known a very fast evolution: going from the Web 1.0, known as Web of Documents where users are merely consumers of static information, to the more dynamic Web 2.0, known as social or collaborative Web where users produce and consume information simultaneously, and entering the more sophisticated Web 3.0, known as the Semantic Web by giving information a well-defined meaning so that it becomes more easily accessible by human users and automated processes. Fostering service intelligence and atomicity (the ability of autonomous services to interact automatically), remains one of the most upcoming challenges of the Semantic Web. This promotes the dawn of a new era: the Intelligent Web (Web 4.0), known as the Internet of Things (IoT), an extension of the Semantic Web where (physical/software) objects and services autonomously interact in a multimedia virtual environment, provided with embedded communication capabilities, common semantics and addressing schemes, promoting the concept of Digital Web Ecosystems where every where (human and software) agents collaborate, interact, compete, and evolve autonomously in order to automatically solve complex and dynamic problems. This paper briefly describes the recent evolution of the Web providing an overview of the technological breakthroughs contributing to this evolution, covering: knowledge bases and semantic data description, XML-based data representation and manipulation technologies (i.e., RDF, RDFS, OWL, and SPARQL) as well as the main challenges toward achieving the Intelligent Web: connectivity, semantic heterogeneity, collective knowledge management, collective intelligence, as well as data sustainability and evolution. We also present some of the main application domains characterizing the Intelligent (Semantic) Web, from information retrieval and content analysis, to systems status monitoring and improving business life-cycle through ubiquitous computing.