The first Web information services were based on traditional information retrieval (IR) algorithms and techniques. However, IR algorithms were developed for smaller and more coherent collections than the Web is. Thus Web searching requires new techniques - exploiting linkage among Web pages or extensions of the old ones, for example. This article offers an overview of today's search engine architectures and techniques in the context of IR. The authors introduce three such architectures and describe their basic components. Then they discuss the most important feature of each Web search process: page importance and its use in retrieval. Some issues and challenges in Web search engines are also summarized as well as considerations on the future of Web searching in terms of the so-called semantic Web.