This article deals with the function of general Web archives within the emerging organization of fast growing digital knowledge resources. It opens with a brief overview of reasons why general Web archives are needed. Sections 2 and 3 present major, long termed Web archive initiatives and discuss the purposes and possible functions and asking how to meet unknown future needs, demands and concerns. Section 4 analyses three main principles for the selection of materials to be preserved in contemporary Web archiving strategies, topic centric, domain centric and time-centric archiving strategies and discusses how to combine these to provide a broad and rich archive. Section 5 is concerned with inherent limitations and why Web archives are always flawed. The last section deals with the question whether and how Web archives may be considered a new type of knowledge organization system (KOS) necessary to preserve Web materials, to allow for the development of range of new methodologies, to analyse these particular corpora in long term and long tail perspectives, and to build a bridge towards the rapidly expanding, but fragmented landscape of digital archives, libraries, research infrastructures and other sorts of digital repositories.